Method and apparatus for providing host resources for an electronic commerce site

A method and apparatus for detecting a change in the operational status of a first host computer and automatically configuring a second host computer to provide additional computing resources that replace or complement the first host computer. In one embodiment, a controller is provided that is capable of detecting a malfunction or failure of the first computer and automatically configuring a second host computer to replace the first host computer. In another embodiment, the controller is capable of detecting changes in the performance of the first host computer and automatically configuring a second host computer to provide additional computing resources for the first host computer. In a further embodiment, both of these techniques can be used to support an electronic commerce site and provide the electronic commerce site with failsafe operation and virtually unlimited computational resources.

FIELD OF THE INVENTION

The present invention is directed to information storage systems, and more particularly, to an information storage system that is capable of detecting a change in the operational status of a first host computer and changing the operation of a second host computer in response to the detected change.

DESCRIPTION OF THE RELATED ART

Providing replacement computer resources for a failed computer resource is termed site failover. Site failover is but one conventional example of a renewable host resource. Site failover from one computer system to another has historically been an expensive and labor intensive procedure. For example, to provide site failover for a first or primary computer system, a complete secondary or failover computer system was traditionally required. In the event of a failure of the primary computer system, the failover computer system would be brought up for use as a temporary replacement of the primary computer system, while the primary computer system was repaired.

To ensure that the failover computer system was a viable replacement for the primary computer system, data on the primary computer system would be periodically copied or backed up to the failover computer system for use in the event of failure of the primary computer system. Typically this back up would be performed manually over a network, or by tape, CD, or diskette. To facilitate site failover, the primary and failover computer systems were typically required to be identical, in terms of both hardware and software. In addition, to ensure that the failover computer system would be ready when needed, the failover computer system was typically maintained in an off state, until needed for replacing the primary computer system upon the failure of the primary computer system.

Years ago, site failures were typically due to a failure of the storage system to which a host computer was attached, rather than a failure of the host computer itself. This is because the storage system was frequently one of the least reliable components of the computer system. With the advent or more reliable storage systems featuring more reliable disk drives and other storage devices, data mirroring, data striping, etc., site failures are now more frequently caused by a failure in the host computer, rather than the storage system to which it is attached.

The use of more reliable storage systems has reduced some of the labor associated with site failover. Even so, some amount of manual intervention is still required. For example, when a failure occurs in a primary host computer, a new failover host computer still needs to be manually brought up in its stead. This typically requires powering down the primary host computer and the storage system, reconfiguring cables that were previously connected between the primary host computer and the storage system to reconnect them between the failover host computer and the storage system, powering on the failover host computer system and the storage system, and then bringing the failover host computer up on-line as a replacement for the primary host computer.

Although the use of more reliable storage systems can dispense with the need for a complete failover computer system (i.e., failover host computer and failover storage system), conventional methods of site failover are expensive. For example, because some amount of manual intervention is still involved, conventional methods of site failover require skilled personnel to be on hand while the primary host computer is operational to effect site failover, when necessary. In addition, most conventional methods of site failover still require that the primary host computer and the failover host computer be identically configured in terms of both hardware and software to facilitate site failover. This duplication of resources is expensive, both initially and in terms of upgrades. For example, when advances in computer technology render a primary host computer obsolete, the identically configured failover host computer is also rendered obsolete. Furthermore, because the failover host computer is typically maintained in a powered-off state until needed, a great deal of computing resources are wasted.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method and apparatus for automatically configuring additional resources for a host computer is described. In one embodiment, a method is provided that includes acts of detecting a change in operation of a first host computer, and automatically configuring a second host computer to provide additional computational resources for the first host computer in response to the act of detecting.

According to another embodiment of the present invention, a computer system is provided. The computer system includes a first host computer, a second host computer, and a controller that is operatively coupled to the first host computer and the second host computer. The controller automatically configures the second host computer to provide additional computational resources for the first host computer in response to a change in operation of the first host computer.

According to another embodiment of the present invention, a computer system is provided that includes a first host computer, a second host computer, and configuration means, coupled to the first host computer and the second host computer, for automatically configuring the second host computer to provide additional computational resources for the first host computer in response to a change in operation of the first host computer.

According to another embodiment of the present invention, a storage system for use with a first host computer and a second host computer is provided. The storage system includes a first storage device to store data of the first host computer, and a controller that is coupled to the first storage device. The controller, when operatively coupled to the first host computer and the second host computer, automatically configures the second host computer to use the data of the first host computer and provide additional computational resources for the first host computer in response to a change in operation of the first host computer.

According to another aspect of the present invention, a method and apparatus for performing load balancing is described. In one embodiment, a method is provided that includes acts of detecting a decrease in performance of a first host computer, and automatically configuring a second host computer to provide additional computational resources for the first host computer in response to the act of detecting.

According to another embodiment of the present invention, a computer system is provided. The computer system includes a first host computer, a second host computer, and a controller that is operatively coupled to the first host computer and the second host computer. The controller automatically configures the second host computer to provide additional computational resources for the first host computer in response to a decrease in performance of the first host computer.

According to another embodiment of the present invention, a computer system is provided that includes a first host computer, a second host computer, and configuration means, coupled to the first host computer and the second host computer, for automatically configuring the second host computer to provide additional computational resources for the first host computer in response to a decrease in performance of the first host computer.

According to another embodiment of the present invention, a storage system for use with a first host computer and a second host computer is provided. The storage system includes a first storage device to store data of the first host computer, and a controller that is coupled to the first storage device. The controller, when operatively coupled to the first host computer and the second host computer, automatically configures the second host computer to use the data of the first host computer and provide additional computational resources for the first host computer in response to a decrease in performance of the first host computer.

According to a further aspect of the present invention, a method and apparatus for performing electronic commerce is described. In one embodiment, a method of performing electronic commerce includes acts of hosting an electronic commerce site on a first host computer, detecting a change in operation of the electronic commerce site, and automatically configuring a second host computer to host at least a portion of the electronic commerce site on the second host computer in response to the act of detecting.

According to another embodiment of the present invention, a computer system is provided. The computer system includes a first host computer that hosts an electronic commerce site, a second host computer, and a controller that is operatively coupled to the first host computer and the second host computer. The controller automatically configures the second host computer to host at least a portion of the electronic commerce site on the second host computer in response to a change in operation of the electronic commerce site.

According to another embodiment of the present invention, a storage system for use with a first host computer and a second host computer is provided. The storage system includes at least one first storage device to store data of the first host computer corresponding to an electronic commerce site hosted by the first host computer, and a controller that is coupled to the at least one first storage device. The controller when operatively coupled to the first host computer and the second host computer, automatically configures the second host computer to use at least a portion of the data of the first host computer that corresponds to the electronic commerce site to host a portion of the electronic commerce site on the second host computer in response to a change in operation of the electronic commerce site.

DETAILED DESCRIPTION

Embodiments of the present invention will be understood more completely through the following detailed description which should be read in conjunction with the attached drawings in which similar reference numbers indicate similar structures.

Embodiments of the present invention are broadly directed to a method and apparatus for providing renewable host resources in a networked computing environment. Within this disclosure, the term “networked computer environment” includes any computing environment in which a plurality of host computers are connected to one or more storage systems in such a manner that the storage system(s) can communicate with each of the host computers. One type of network in which embodiments of the present invention may be used is a Fibre Channel network, although the present invention is not so limited. For example, other network configurations and protocols may be used, such as Ethernet, FDDI, Token Ring, etc. Embodiments of the present invention may be used in Local Area Networks (LANS) as well as Wide Area Networks (WANS), with no requirement that the host computers or the storage system(s) reside in the same physical location, the same network segment, or even in the same network. Moreover, embodiments of the present invention may also be used with conventional point-to-point storage connections, such as SCSI, ESCON, etc. that are not typically viewed as a “network”. In this regard, all that is necessary is that the storage system be capable of communicating with each host computer that is part of the renewable host resource environment, as will be described further below.

According to one aspect of the present invention, renewable host resources are provided that can be automatically (e.g., without any manual intervention by a system administrator or other personnel) configured and put into use when a change in the operational status of a host computer is detected. In one embodiment of the present invention, these renewable host resources are provided in the form of a secondary or failover host computer that can be automatically configured and brought on line to replace a failing primary host computer. In other embodiments of the present invention, the renewable host resources do not replace a primary host computer, but rather complement the operation of a primary host computer. In particular, these other embodiments of the present invention permit additional host computing resources to be dynamically configured and then added to and/or removed from the computer network dependent upon an operational status of the primary host computer. For example, when processing activity, memory utilization, etc. on a primary host computer reaches a threshold where the performance of the primary host computer is impacted, one or more additional host computers can be configured and brought on line to share the computational load.

According to a further aspect of the present invention, there is no requirement that the primary host computer or the secondary host computer(s) be identically configured, either in software or hardware. Furthermore, although embodiments of the present invention are described in terms of primary and secondary host computers, the present invention is not so limited. In this regard, the present invention may be used to provide renewable host resources for a computer site that includes a plurality of host computers. Moreover, as with individual host computers, the present invention is not limited to computer sites that reside in the same physical or network location, as primary and secondary computer sites may reside in different geographic locations.

FIG. 1depicts one illustrative networked computing environment in which embodiments of the present invention may be used. As shown inFIG. 1, networked computing environment100includes a primary host computer110and a secondary host computer120. As used herein, the term “host computer” refers to any computer that includes at least one processor, such as a personal computer (PC), a workstation, a mainframe, a networked client, etc., that is capable of communicating with other devices, such as a storage system or other host computers. The primary and secondary host computers110,120communicate with each other over a communication network140, such as Ethernet, Token Ring, Fibre Channel, etc. Each of the host computers110,120is also connected to a storage system130by a respective connection145A,145B. Connections145A and145B may include a bus connection, such as SCSI or ESCON, or may include networked connections such as Fibre Channel. There is no requirement that connection145A use the same type of connection or protocol as connection145B. For example, connection145A may use a point-to-point connection such as SCSI, while connection145B may use a network connection such as Fibre Channel. Moreover, it should be appreciated that connections145A and145B may be implemented via the communication network140.

As shown inFIG. 1, storage system130includes one or more storage devices135(e.g., disk drives) to service the storage needs of the host computers110,120. Storage devices135may include one or more disks of a recording medium, such as a magnetic recording medium or an optical recording medium. The storage devices may also include solid state storage devices, such as RAM-disks, as an alternative to or in addition to, more conventional forms of recording media. One example of a storage system that may be used with embodiments of the present invention is the SYMMETRIX line of storage systems available from EMC Corporation of Hopkinton, Mass. The SYMMETRIX line of storage systems is described in numerous publications from EMC corporation, including the SYMMETRIX model 55XX product manual, P-N200-810-550, rev. F, February, 1996. However, it should be appreciated that the present invention is not limited to the use of a SYMMETRIX storage system, as other storage systems may alternatively be used.

Storage system130also includes one or more port adapters132A,132B to connect to the primary and secondary host computers110,120, a storage processor or controller133, and one or more disk adapters (not shown) that are operatively coupled to the storage devices135. As the detailed structure of the storage system130is not necessary to understanding the present invention, and as the invention is not limited to any particular structure, further description of the storage system130is omitted herein.

According to one aspect of the present invention, computing environment100also includes a controller160that is operatively coupled to the primary host computer110, the secondary host computer120, and the storage system130. In one embodiment of the present invention, the controller160is implemented in software executing on storage processor133. In this embodiment, the controller160communicates with the primary and secondary host computers over connections145A and145B. As noted above, connections145A and145B may be point-to-point connections such as SCSI, ESCON, or network connections, such as Fibre Channel. Alternatively, controller160may be implemented separately from the storage system130, for example, in a separate processor, as shown in FIG.1. Where controller160is implemented separately from the storage system130, controller160may communicate with the primary host computer110, the secondary host computer120, and the storage system130over connections165A,165B, and165C as shown in dotted line form. Connections165A,165B, and165C may be separate point-to-point connections, or network connections. Indeed, all that is necessary is that controller160be capable of communicating with the primary host computer110, the secondary host computer120, and the storage system130.

Controller160is capable of automatically detecting a change in the operational status of the primary host computer110and, in response to this change in operational status, automatically altering the operational status of the secondary host computer120. As used herein, the term “automatically” means without any manual intervention by a system administrator or other personnel. According to one embodiment of the present invention, controller160periodically queries the primary host computer110to determine its operational status. Based upon the response to this query, or the lack of a response to this query within a predetermined timeframe, the controller160can determine whether the operational status of the secondary host computer should be changed to provide additional host resources to complement or replace those provided by the primary host computer110.

According to one embodiment to the present invention, controller160may be configured as a failover controller to configure and bring on-line secondary host computer120as a replacement for primary host computer110in the event that primary host computer110fails. When a failure of the primary host computer110is detected, controller160configures the secondary host computer120as a replacement for the primary host computer110, shuts down the primary host computer110, and then brings the secondary host computer120on line as a replacement to the primary host computer110. Although controller160is capable of detecting the failure of the primary host computer110, the controller160can also be capable of detecting malfunctions or other errors in the primary host computer110that do not amount to a complete failure. For example, malfunctions that may be detected include CPU errors or memory errors on the primary host computer110, the malfunctioning of a network controller, an I/O controller, or adapter, or any other type of malfunction indicative of a diminished operational capacity of the primary host computer110. In particular, in one embodiment of the present invention, controller160is capable of detecting malfunctions in the primary host computer110that are indicative of an imminent failure of the primary host computer110. By detecting the imminent failure of the primary host computer110prior to actual failure, any data that is stored locally on the primary host computer110can be written to the storage system130, and the primary host computer110can be shut down in an orderly manner. This reduces the possibility of lost data.

According to another embodiment of the present invention, an agent162is provided for the primary host computer110and communicates with the controller160. In one embodiment, the agent162is implemented in software that executes on a processor in the primary host computer110. The agent162monitors the operation of the primary host computer110and reports any errors to the controller160. For example, agent162can monitor system error messages generated by the primary host computer110and report these messages to the controller160. Alternatively, or in addition to monitoring error messages, the agent162can periodically run diagnostic tests on the primary host computer110to verify the operation of the primary host computer110. It should be appreciated that varying levels of diagnostic tests may be run at different time intervals. For example, relatively quick diagnostic routines that are capable of detecting serious problems may be executed at shorter time intervals, while more extensive diagnostic routines capable of detecting less obvious or severe problems may be executed at longer time intervals. The agent162may include sophisticated detection routines that are capable of identifying a series of relatively minor errors that, over time, may indicate the imminent failure of one or more components of the primary host computer110.

In one embodiment, the agent162is programmed to send a status report to the controller160at predetermined periodic intervals, irrespective of whether errors have been detected on the primary host computer110. In this embodiment, when a status report has not been received by the controller160at an expected interval, the controller160assumes that the primary host computer110has failed and responds appropriately. As previously described, when a failure is detected by the controller160, the controller160may shut down the primary host computer110and configure the secondary host computer120to act in its stead.

According to one embodiment of the present invention, the networked computer environment100may also include one or a number of relays170,171that are coupled to the controller160, a respective host computer, and a power supply (not shown) of the respective host computer. For example, relay170may be coupled between the primary host computer110, the controller160, and a power supply of the primary host computer110, and relay171may be coupled between the secondary host computer120, the controller160, and a power supply of the secondary host computer120. Each relay170,171can be switched between a first state in which no power is supplied to the respective host computer, and a second state in which power is supplied to the respective host computer. In one embodiment, after the primary host computer110is shut down in an orderly manner, or after it is determined that an orderly shutdown is not possible, controller160can issue a command to relay170instructing the relay170to switch from the second state to the first state and cut-off power to the primary host computer110. This ensures that the primary host computer110is no longer active on the network140. Similarly, controller160can issue a command to relay171instructing the relay171to switch from the first state to the second state to provide power to the secondary host computer120. This permits the secondary host computer120to be brought on-line as a replacement to the primary host computer110without any manual intervention (i.e., automatically).

A flow diagram illustrating one implementation of a site failover routine that may executed by the controller160ofFIG. 1is now described with respect to FIG.2A. For purposes of illustration, it is assumed that the primary and secondary host computers110,120are identical in terms of hardware, and that the primary and secondary host computers110,120are located in the same LAN (i.e., communication network140). Because the primary and secondary host computers110,120have identical hardware configurations, each is capable of using the exact same data (operating system data, application programs, and application program data) without modification. However, as will be described further below, the invention is not limited to use with identical host computers, nor is it limited to primary and secondary host computers that are located in the same LAN.

At step210, the failover routine awaits the detection of a malfunction or failure of the primary host computer110. As noted above with respect toFIG. 1, this may be detected in any number of ways, such as by being informed by an agent162of the primary host computer110that a malfunction or failure was detected or is imminent, by not receiving a status message from the agent162within a particular time interval, or by the controller160actively querying the primary host computer110as to its status. When it is determined at step210that no failure or imminent failure has been detected, the failover routine simply waits at step210. Alternatively, when a failure or imminent failure is detected at step210, the routine proceeds to step220.

At step220the site failover routine performs an orderly shutdown of the primary host computer110if this is at all possible. For example, the controller160can be provided with the appropriate privileges on the primary host computer110so that, as long as the primary host computer110is capable of responding, the controller160can issue a command to the primary host computer110to perform an orderly shutdown. The form of the shutdown command will of course vary, depending upon the operating system used by the primary host computer110. It should be appreciated that in many instances the failure of the primary host computer110may be such that an orderly shutdown of the primary host computer110is not possible, either due to an inability of the storage system130to communicate with the primary host computer10, or for some other reason. When an orderly shutdown of the primary host computer110is not possible, step230may be omitted. However, it should be appreciated that an orderly shutdown of the primary host computer110will typically be attempted, as an orderly shutdown helps to ensure that the primary host computer110is no longer an active participant on the network. In addition, an orderly shutdown will generally cause any outstanding changes to data that is to stored locally in the primary host computer to be written to the storage system, so that the data stored on the storage system130is current.

In the event that the primary host computer110cannot be shutdown in an orderly manner, or in addition to shutting down the primary host computer10in an orderly manner, the controller160may also issue a command to relay170instructing the relay170to switch off power to the primary host computer110. This ensures that the primary host computer10is no longer an active participant on the network.

After shutting down the primary host computer110at step220, the site failover routine proceeds to step230, wherein the data of the primary host computer10is replicated or copied to another storage device135of the storage system that can be accessed by the secondary host computer120. In one embodiment, the data that is replicated at step230includes the operating system, as well as any application programs and application program data of the primary host computer110. In this embodiment, each volume of data of the primary host computer110is copied to a corresponding volume of data on a storage device135that can be accessed by the secondary host computer120(e.g., a storage device135that can be accessed via port adapter132B). In another embodiment, this replication of data is performed by splitting off a mirrored copy of each volume of data of the primary host computer10that is mirrored to a corresponding volume of data that is accessible to the secondary host computer120.

After replicating the data of the primary host computer10, the routine proceeds to step240, wherein the site failover routine powers on the secondary host computer120and brings the secondary host computer120on line as an identical replacement to the primary host computer110. The secondary host computer thus utilizes the replicated data (operating system data, application programs, and application program data) of the primary host computer110as if it were its own. In one embodiment, where the primary host computer110is configured to automatically boot to an on-line state upon power up, step240may be performed without any manual intervention. For example, controller160may issue a command instructing relay170to switch from the first state in which no power is supplied to the second host computer120to the second state in which power is supplied to the secondary host computer120. As the primary host computer110and secondary host computer120share the same hardware configuration and can use the exact same data, the secondary host computer120will be automatically brought on-line as a replacement for the primary host computer110upon the application of power.

Alternatively, where the primary host computer110is not configured to automatically boot to an on-line state upon power up, an additional step may be required to bring the secondary host computer120on-line as a replacement for the primary host computer110. For example, many host computers are configured to boot to a standalone state after the application of power. On a host computer running a Unix operating system, such a standalone state is termed single-user mode. In this stand alone state, the host computer can be instructed to perform certain limited commands, and is capable of certain low-level communication with peripheral devices (such as a control console or a storage system, for example), but is not a participant on the network. Typically such host computers require that an additional command be manually entered from a control console that is attached to the host computer to bring the host computer from the stand-alone state to an on-line state.

However, according to another embodiment of the present invention, this additional command may be provided to the secondary host computer120automatically by the controller160. For example, after instructing relay170to supply power to the secondary host computer120, the controller160may issue an appropriate command (e.g., boot or b) to the secondary host computer120to bring it from a stand alone state to an online state. In this manner, the secondary host computer120can be automatically brought on-line as a replacement for the primary host computer110. After bringing the secondary host computer120on line as a replacement for the primary host computer110in step240, the routine terminates.

The flowchart ofFIG. 2Ais but one example of a site failover routine according to the present invention. It should be appreciated that many variations and modifications to this routine are possible. For example, rather than utilizing relays170and171to automatically power-off the primary host computer110and automatically power-on the secondary host computer120, one or more of these steps may be performed manually. Such a modification still avoids the reconfiguration of cables and the backing up of data of the primary host computer110to the secondary host computer120that is conventionally required.

It should be appreciated that the step of replicating the data of the primary host computer110need not be performed after the detection of a malfunction or failure of the primary host computer110at step210, as it may be performed may prior to a detected failure. For example, the data of the primary host computer110may be replicated at any time prior to a malfunction or failure of the primary host computer110, such as shortly after the primary host computer110is booted and on-line. The replicated data may also be periodically updated, prior to a detected malfunction or failure of the primary host computer110, to reflect any changes made to the data of the primary host computer110during operation. This ensures that the replicated data is as current as possible. Upon the detection of a malfunction or failure of the primary host computer110, the data that was replicated (and perhaps also updated prior to the detected malfunction or failure) can then be updated to reflect any additional changes that were made to the data of the primary host computer110prior to the detected failure or malfunction. The updating of the replicated data may, for example, be performed using an incremental update facility, such as the Symmetrix Differential Data Facility (SDDF), available from EMC Corporation of Hopkinton Mass., that updates only data that has changed.

Furthermore, rather than replicating all of the data of the primary host computer110at step230, only certain data may be replicated. For example, where the operating system of the primary host computer110is stored in a separate volume or storage device from the rest of the data (e.g., application programs and application program data), the operating system can be replicated at a time prior to a malfunction or failure of the primary host computer110, and the remaining data of the primary host computer110can be replicated thereafter. Because the operating system of a host computer changes only infrequently, the operating system of the primary host computer10can be replicated for use by the secondary host computer120prior to a detected failure, and the secondary host computer120powered on and booted to a standalone state in advance of a detected failure. When a failure of the primary host computer110is detected, the primary host computer110can be shutdown, the remaining data (e.g., application programs and application program data) of the primary host computer110replicated, and the secondary host computer120brought on-line as a replacement to the primary host computer110. Advantageously, this may be performed in a shorter amount of time than the routine ofFIG. 2Abecause any power-up diagnostic routines that are typically executed upon power up of the secondary host computer120will have already been completed. Moreover, the secondary host computer120can be automatically brought on line as a replacement to the primary host computer110from a standalone state without the use of relay171.

Where the operating system of the primary host computer110is replicated in advance of a detected failure, it should be appreciated that the primary and secondary host computers110,120will each have identical node names, domain names, network addresses, etc. Thus, care must be taken to ensure that the secondary host computer120is maintained in a standalone state as long as the primary host computer110is operational, as network problems may ensue if the two host computers with identical network identities were simultaneously operational on the same network. As an alternative to maintaining the secondary host computer120in a standalone state, after replicating the operating system of the primary host computer110, the secondary host computer120may be powered on and brought to a standalone state, and then dynamically configured in the standalone state to have a different host name, domain name, network address etc. than the primary host computer110. The secondary host computer120may then be brought on line with this new identity. Upon the detection of a failure of the primary host computer110, the secondary host computer may be shutdown to a standalone state, the configurable parameters (e.g., node name, domain name, network address, etc) of the secondary host computer120dynamically reconfigured to be the same as the primary host computer110, the remaining data replicated, and the secondary host computer120rebooted and brought on line as a replacement for the primary host computer110.

It should be appreciated that although the flowchart ofFIG. 2Aincludes a step of replicating data (i.e., step230), the present invention is not so limited. In this regard, rather than replicating the data of the primary host computer110at step230, the controller160may instead modify the assignment of storage devices135used by the primary host computer110so that those storage devices are accessible to the secondary host computer120. For example, referring toFIG. 1, the controller160can instruct the storage processor133to modify the assignment of those storage devices135assigned to port adapter132A so that they are instead assigned to port adapter132B. With this modification, no data replication is required, and the secondary host computer120can directly access the data of the primary host computer110.

Other modifications may also be made to the site failover routine of FIG.2A. For example, where the primary host computer110fails in a manner in which it is not shutdown in an orderly fashion resulting in a loss of data, the controller160can perform additional steps enabling the secondary host computer120to utilize a backup copy of data used by the primary host computer110. That is, rather than using the data of the primary host computer110that was replicated in step230, the controller160can utilize different data, such as the most recent known-good backup of data from the primary host computer110. This data may be resident on other storage devices135of the storage system130, or may be copied from another storage system (not shown) for this purpose. For example, prior to a failure of the primary host computer110, the controller160may be provided with a location, on storage system130or elsewhere on the network, where the most recent known-good backup copy of data of the primary host computer110is kept. If, after attempting to shutdown the primary host computer at step220, the controller160determines that the primary host computer110was not shutdown in an orderly fashion, or that the data of the primary host computer110has been corrupted, the controller160can replicate the most recent backup copy of data of the primary host computer110.

It should be appreciated that even the use of a backup copy of data of the primary host computer110by the secondary host computer120may still result in a loss of data. For example, any data of the primary host computer110that was changed since the most recent backup of the primary host computer110will not have been backed up, and thus, would not be available for use by the secondary host computer120. However, the amount of data that is lost can be minimized. For example, many applications maintain a transaction log file that identifies changes made to application data since the most recent back-up of that application data. One such application program having this capability is ORACLE database software, which maintains a transaction log file that identifies changes made to the ORACLE database. Where an application program maintains such a transaction log file, any changes that are identified in the log file can be applied to the backup copy of data prior to bringing the secondary host computer120on-line for use as a replacement to the primary host computer110.

Another exemplary implementation of a site failover routine that may executed by the controller160ofFIG. 1is now described with respect to FIG.2B. This site failover routine is particularly well suited for use with database applications such as ORACLE and SQL that maintain transaction log files which may be used to update the database. Again, for purposes of illustration, it is assumed that the primary and secondary host computers110,120are identical in terms of hardware and located in the same LAN (e.g., communication network140), although the present invention is not so limited.

At step205the data of the primary host computer110is replicated or copied to another storage device135of the storage system that is accessible to secondary host computer120. In one embodiment, each volume of data of the primary host computer110is copied to a corresponding volume of data on a storage device135that can be accessed by the secondary host computer120(e.g., a storage device135that can be accessed via port adapter132B). In another embodiment, this replication of data is performed by splitting off a mirrored copy of each volume of data of the primary host computer110that is mirrored to a corresponding volume of data that is accessible to the secondary host computer120. In one embodiment, the data that is replicated at step205includes all of the data of the primary host computer110that is stored on the storage system130, including the operating system as well as any application programs and application program data. It should be appreciated that this step of replicating may be performed any time prior to failure or malfunction of the primary host computer110, and that the present invention is not limited to a replication of all of the data of the primary host computer110. After replicating the data of the primary host computer110, the routine proceeds to step210.

At step210, the failover routine awaits the detection of a malfunction or failure of the primary host computer10in a manner similar to that described with respect to FIG.2A. When it is determined at step210that no failure or imminent failure has been detected, the failover routine simply waits at step210. When a failure or imminent failure is detected at step210, the routine proceeds to step220.

At step220the site failover routine performs an orderly shutdown of the primary host computer110in a manner similar to that described with respect to FIG.2A. After shutting down the primary host computer10, the routine proceeds to step225, wherein the controller160locates the transaction log file and applies that transaction log file to the appropriate application program data that was replicated in step205. The transaction log file can be located by the controller by using the mapping techniques described in copending U.S. patent application Ser. No. 09/107,538, entitled METHOD AND APPARATUS FOR GRAPHICALLY DISPLAYING MAPPING OF A LOGICAL OBJECT, filed Jun. 30, 1998, and commonly assigned to EMC Corporation of Hopkinton, Mass., which is hereby incorporated by reference in its entirety. The transaction log file is applied to update the application program from the time that the data was replicated at step205. After applying the transaction log file in step225, the routine proceeds to step240, wherein the secondary host computer120is powered on and brought on line in a manner similar to that described with respect to FIG.2A. The routine then terminates.

The site failover routine ofFIG. 2Bpermits the database application program data that is used by the secondary host computer120to be as up-to-date as possible. Furthermore, because the majority of the data of the primary host computer110(i.e., the operating system, the application program, and most of the application program data) is replicated prior to the failure of the primary host computer110, when a failure is detected, this site failover routine can be performed in little more than the time it takes to locate and apply the transaction log file to the replicated data. Examples of systems on which aspects of the present invention can be employed to provide site failover include a SUN workstation running Oracle version 7.3.4 database software with version 2.5.1 or 2.6 of the SUN Solaris operating system, and a Intel Pentium computer running SQL 6.5 on Windows NT, version 4.0.

It should be appreciated that in both the previously described site failover routines, where a mirror copy of the data of the primary host computer110is used by the secondary host computer120, any changes made by the secondary host computer to that split-off mirrored copy of data may be identified so that these changes can be applied to the data of the primary host computer110when it resumes operational status.

Another exemplary implementation of a site failover routine that may be executed by the controller160ofFIG. 1is now described with respect to FIG.2C. As in the flowcharts ofFIGS. 2A and 2B, it is again assumed, for purposes of illustration, that the primary and secondary host computers110,120are identical in terms of hardware and that the primary and secondary host computers110,120are located in the same LAN. However, in contrast to the site failover routine ofFIGS. 2A and 2Bwhere the secondary host computer120was initially in a powered off state, in this embodiment, both the primary and secondary host computers1110,120may be fully operational on the same LAN, each with their own separate identities. In this embodiment, it is assumed that the secondary host computer120maintains a mirror copy of its data on other storage devices, although, as described further below, the present invention is not so limited. It should be appreciated that the data of the secondary host computer120may be mirrored to other storage devices135of storage system130(i.e., a local mirror) or to other storage devices135of a different storage system (not shown) that can communicate with storage system130.

At step210, the failover routine awaits the detection of a malfunction or failure of the primary host computer110in a manner similar to that described with respect toFIGS. 2A, and2B. When it is determined at step210that no failure or imminent failure has been detected, the failover routine simply waits at step210. Alternatively, when a failure or imminent failure is detected at step210, the routine proceeds to step220.

At step220the site failover routine performs an orderly shutdown of the primary host computer110in a manner similar to that described with respect to FIG.2A. To ensure that the primary host computer110is no longer an active participant on the network, the controller160may also issue a command to instruct relay170to turn off power to the primary host computer110. After shutting down the primary host computer110, the site failover routine proceeds to step222, wherein the secondary host computer120is shutdown in an orderly manner. This can be performed, for example, by notifying all users of the secondary host computer120that the secondary host computer120is being shutdown, instructing all users to log out of the secondary host computer120, and then shutting down the secondary host computer120to bring it to a stand alone state. During such an orderly shutdown, any data that was resident in local memory of the secondary host computer120would then be flushed to the storage system130. It should be appreciated that the above-described order of performing steps220and222may, of course, be reversed.

After shutting down the secondary host computer120, the site failover routine issues an instruction to the storage system130to break or discontinue the mirroring of the data of the secondary host computer120. Thus, from this point onward, any changes made to the primary copy of the data of the secondary host computer120will no longer be replicated to the mirrored copy. After instructing the storage system130to break the mirroring of data, the site failover routine proceeds to step226, wherein power to the secondary host computer120is turned off. This step may be performed automatically by issuing a command to relay171, or alternatively, may be performed manually. After shutting off power to the secondary host computer120, the routine proceeds to step230, wherein the data of the primary host computer110is replicated or copied to the secondary host computer120in a manner similar to that described with respect toFIGS. 2A and 2B. As should be appreciated, this step of replicating the data of the primary host computer110overwrites the primary copy of the data of the secondary host computer120. However, because mirroring of the data of the secondary host computer was terminated at step224, this replication does not affect the mirrored copy of the data of the secondary host computer120. As a result, after the primary host computer110is returned to operational status, the data of the secondary host computer120that has been preserved on the split-off mirror copy can be copied back to its original location, and the secondary host computer120returned to normal operational status.

After replicating the data of the primary host computer110, the routine proceeds to step240, wherein the secondary host computer120is either manually or automatically powered on and brought on line as a replacement to the primary host computer110, wherein the routine terminates.

Advantageously, the site failover routine ofFIG. 2Cpermits both the primary and secondary host computers110,120to be fully operational prior to a detected failure of the primary host computer110. Moreover, both the primary and secondary host computers110,120may have separate and independent identities prior to a detected failure. As a result, the computing resources of the secondary host computer120may be used to their full potential and need not be wasted by sitting idle or in a powered off condition waiting for the advent of a failure of the primary host computer120.

Although the site failover routine ofFIG. 2Cwas described in terms of a secondary host computer120that utilized data mirroring, it should be appreciated that the present invention is not so limited. For example, where the secondary host computer120does not use data mirroring, the site failover routine ofFIG. 2Cmay be modified to make a backup copy of the data of the secondary host computer120prior to replicating the data of the primary host computer at step230. The backup copy may be a local backup copy (i.e., local to storage system130), or may be a remote backup copy (i.e., to a storage system other than storage system130). Such a step of backing up the data of the secondary host computer120may be performed, for example, instead of step224. Alternatively, where the data of the secondary host computer120has been recently backed up, or where the data of the secondary host computer120is not critical, step224ofFIG. 2Cmay be omitted.

It should be appreciated that the replication of data that is performed in each of the site failover routine ofFIGS. 2A-Cmay be performed without any involvement of the primary host computer110. In particular, in a conventional site failover routine, the primary host computer110would be intimately involved in copying data from the storage devices used by the primary host computer110to those used by the secondary host computer120. In contrast, in the embodiments ofFIGS. 2A-C, the replication of data is performed by the controller160and without burdening any host computer. It should be appreciated that in conventional methods of site failover that require the participation of the primary host computer110in the replication of data, unless the replication is done prior to the failure of the primary host computer110, data replication may not be possible (e.g., due to a fault in the host computer), or may result in corrupted data.

Although the exemplary site failover routines ofFIGS. 2A,2B, and2C were described in terms of only a single storage system130to which both the primary and secondary host computers110,120were connected, the present invention is not so limited. For example,FIG. 3illustrates a networked computing environment300in which the primary and secondary host computers110,120are connected to different storage systems130and130′, respectively. Primary host computer110communicates with storage system130over connection145A, and secondary host computer120communicates with storage system130′ over connection145B. Controller160is capable of communicating with each of the host computers110,120, and each of the storage systems130,130′. Controller160may be implemented in software executing on a storage processor133(FIG. 1) in one of the storage systems130or130′, or may be implemented separately from the storage systems, as shown. In a manner similar to that described with respect toFIG. 1, controller160may communicate with the primary host computer110, the secondary host computer120and the storage systems130and130′ over point-to point connections, or network connections, or a combination of point-to-point and network connections. In this regard, all that is necessary is that the controller160be capable of communicating with each host computer110,120and each storage system130,130′.

In a manner similar to that of the computer environment100ofFIG. 1, networked computer environment300may also include one or a number of relays170,171that are coupled to the controller160, a respective host computer, and a power supply (not shown) of the respective host computer. Each relay170,171can be switched between a first state in which no power is supplied to the respective host computer, and a second state in which power is supplied to the respective host computer.

An exemplary flow diagram illustrating one implementation of a site failover routine that may be executed by the controller160ofFIG. 3is now described with respect to FIG.4. The site failover routine ofFIG. 4is essentially identical to that described above with respect to FIG.2A. However, rather than the data of the primary host computer being replicated to other storage devices135on the same storage system130, the data is instead replicated to the storage devices135′ of a different storage system130′. Again, for purposes of illustration, it is assumed that the primary and secondary host computers10,120are identical in terms of hardware, and that the primary and secondary host computers110,120are located in the same local area network. However, as will be described further below, the present invention is not limited in this regard.

At step410, the failover routine awaits the detection of a malfunction or failure of the primary host computer110. When a failure or imminent failure is detected at step410, the routine proceeds to step-420, wherein the site failover routine performs an orderly shutdown of the primary host computer110, if possible. When an orderly shutdown of the primary host computer110is not possible, step420may be omitted. In the event that the primary host computer110cannot be shutdown in an orderly manner, or in addition to shutting down the primary host computer110in an orderly manner, the controller160may also issue a command to relay170instructing the relay170to switch off power to the primary host computer110in a manner similar to that described above with respect toFIGS. 2A-C. This ensures that the primary host computer110is no longer an active participant on the network. After shutting down the primary host computer110, the site failover routine proceeds to step430.

At step430, the controller160replicates or copies the data of the primary host computer110from storage system130to storage system130′ for use by the secondary host computer120. In one embodiment, all of the data used by the primary host computer110(i.e., the operating system, application programs, application program data, etc.) is replicated for use by the secondary host computer120. In other embodiments, only portions of the data of the primary host computer110are replicated, as described further below. After replicating the data of the primary host computer110, the routine proceeds to step440, wherein the secondary host computer120is powered on and brought on line as an identical replacement to the primary host computer110. After replacing the primary host computer110, the routine terminates.

Although the site failover routine described above with respect toFIG. 4includes a step of replicating the data of the primary host computer110stored on storage system130to storage system130′, the present invention is not so limited. For example, where the secondary host computer120can also communicate with storage system130, the secondary host computer120may simply use the data of the primary host computer110that is stored on storage system130. This may be performed, for example, where connections145A and145B are common network connections. Alternatively, where storage system130′ is used as a mirror for storage system130(for example, by using the Symmetrix Remote Data Facility (SRDF), available from EMC Corporation of Hopkinton, Mass., that allows data to be mirrored among physically different storage systems that can be located in the same, or different, geographic locations), mirrored data of storage system130may already be present on storage system130′. When this is the case, the step of replicating the data of the primary host computer110would be unnecessary. As details of SRDF are described in numerous publications from EMC Corporation, a detailed discussion of this facility is omitted herein.

The site failover routine described with respect toFIG. 4may also be modified in a number of other ways. For example, the secondary host computer120may be on-line prior to being called upon to replace the primary host computer110, as discussed above, and may even have its own network identity, separate and independent from that of the primary host computer110. Moreover, rather than replicating the data of the primary host computer110that is stored on storage system130, the data may be replicated from a backup copy of that data. It should also be appreciated that some of the data (e.g., the operating system) of the primary host computer110may be replicated prior to a detected failure, and the remaining data replicated at a later time, in a manner similar to that described with respect toFIGS. 2A-C.

It should be appreciated that the replication of data that is performed in the site failover routine ofFIG. 4may also be performed without any involvement of the primary or secondary host computers110,120. In particular, in a conventional site failover routine, the primary and secondary host computers110,120would be intimately involved in copying data from the storage system130, transferring that data to the secondary host computer120via tape, diskette, or over the communication network140, and then copying that data from the secondary host computer to storage system130′. In contrast, the site failover routine ofFIG. 4requires little or no involvement of the primary and secondary host computers110,120in replicating this data, as the copying is managed by the controller160.

Each ofFIGS. 1-4was described in terms of a networked computing environment in which identically configured host computers were coupled to the same communication network140. However, embodiments of the present invention are not limited to use on a single communication network, as they may be used in a variety of network topologies. For example,FIG. 5illustrates a networked computing environment in which two identical host computers are connected to different networks.

As shown inFIG. 5, networked computing environment500includes a primary host computer110that is coupled to a first storage system130, a secondary host computer120that is coupled to a second storage system130′, and a controller160that is operatively coupled to the primary and secondary host computers110,120and the first and second storage systems130,130′. The primary and secondary host computers110,120are each coupled to a respective relay170,171, that communicates with the controller160. In a manner similar to that described with respect toFIGS. 1 and 3, each relay170,171is capable of providing power to the respective host computer in a first state and disabling the supply of power to the respective host computer in a second state.

The primary host computer110is coupled to a first communication network140and the secondary host computer120is coupled to a different communication network140′. Communication between networks140and140′ is facilitated by a network connector505. The network connector505may include a router or a bridge, or a number of routers and/or bridges that permit communication between networks140and140′.

The networked computing environment500also includes a network director515that is coupled to communication network140. As known to those skilled in the art, network directors are frequently used for load balancing and are capable of routing connection requests or other communications among a number of host computers. Some network directors are also capable of redirecting connection requests or other communications that are directed to a first host computer (e.g., to a network address of the first host computer) to another host computer (e.g., to a network address of another host computer). Examples of network directors that are capable of redirecting communications from one host computer to another host computer include local directors from Cisco System and Arrowpoint. As the functionality of network directors is well known in the art, a detailed discussion of the network director515is omitted herein.

As in the previously described embodiments ofFIGS. 1-4, controller160may be implemented in software executing on a storage processor133(FIG. 1) in one of the storage systems130,130′, or alternatively, may be implemented separately from the storage systems, as illustrated in FIG.5. Controller160is capable of communicating with the primary and secondary host computers110,120, the first and second storage systems130,130′, and the network director515. Each of these communications may be by dedicated point-to-point connections, by network connections, or a combination of point-to-point and network connections. Controller160is also capable of communicating with each relay170,171. Each relay170,171will typically be located in the same geographic location as the respective host computer to which it is coupled. To control each relay170,171, a communication path between the controller160and each relay170,171is provided. For example, where the controller160and relay170are located in the same geographic location, and relay171is located in a different geographic location, the controller160may communicate with relay170via a direct local connection, and communicate with relay171using a remote connection, for example, by modem. Alternatively, controller160and relay171may be located in the same geographic location with relay170being located in a different geographic location, or both relays170,171may be located in different geographic locations from the controller160.

An exemplary flow diagram illustrating one implementation of a site failover routine that may be executed by the controller160ofFIG. 5is now described with respect to FIG.6. Again, for purposes of illustration, it is assumed that the primary and secondary host computers110,120are identical in terms of hardware, although the present invention is not so limited. In the exemplary site failover routine ofFIG. 6, it is also assumed that the secondary host computer120is fully operational on network140′ with its own identity prior to a detected failure of the primary host computer110, and that the secondary host computer maintains a mirror copy of its data on other storage devices in a manner similar to that of FIG.2C. However, as described further below, the present invention is not so limited.

At step610, the site failover routine awaits the detection of a malfunction or failure of the primary host computer110in a manner similar to that described with respect toFIGS. 2A-C, and4. When it is determined that no failure or imminent failure has been detected, the failover routine simply waits at step610. Alternatively, when a failure or imminent failure is detected at step610, the routine proceeds to step620, wherein the site failover routine performs an orderly shutdown of the primary host computer110, if possible, in a manner similar to that described above. Once again, to ensure that the primary host computer110is no longer an active participant on the network, the controller160may also issue a command to instruct relay170to turn off power to the primary host computer110.

After shutting down the primary host computer110, the site failover routine proceeds to step622, wherein the secondary host computer120is shutdown in an orderly manner. As discussed with respect toFIG. 2Cabove, this can be performed, for example, by notifying all users of the secondary host computer120that the secondary host computer120is being shutdown, instructing all users to log out of the secondary host computer120, and then shutting down the secondary host computer120to bring it to a stand alone state. During such an orderly shutdown, any data that was resident in local memory of the secondary host computer120would then be flushed to the storage system130.

After shutting down the secondary host computer120, the site failover routine proceeds to step624, wherein the controller160issues an instruction to the storage system130′ to break or discontinue the mirroring of the data of the secondary host computer120. From this point onward, any changes made to the primary copy of the data of the secondary host computer120will no longer be replicated to the mirrored copy. After instructing the storage system130′ to break the mirroring of data, the site failover routine proceeds to step626, wherein power to the secondary host computer120is turned off. This step may be performed automatically by issuing a command to relay171, or alternatively, may be performed manually.

After shutting off power to the secondary host computer120, the routine proceeds to step630, wherein the failover routine replicates the data of the primary host computer110that is stored on storage system130to storage system130′ in a manner similar to that described with respect to FIG.4. In one embodiment, all of the data used by the primary host computer110(i.e., the operating system, application programs, and application program data) is replicated to storage system130′ for use by the secondary host computer120. As should be appreciated, this step of replicating the data of the primary host computer110overwrites the primary copy of the data of the secondary host computer120that is stored on storage system130′ with the replicated data of the primary host computer110. However, because mirroring of the data of the secondary host computer120was terminated at step624, this replication does not affect the mirrored copy of the data of the secondary host computer120. As a result, after the primary host computer110is returned to operational status, the data of the secondary host computer120that has been preserved on the split-off mirror copy can be copied back to its original location, and the secondary host computer120returned to normal operational status. After replicating the data of the primary host computer110, the routine proceeds to step634.

At step634, the controller160modifies the replicated data so that the secondary host computer120can use the replicated data and also be accessed via communication network140′. Where the primary and secondary host computers110,120are identical in terms of hardware, the data that is modified at step634corresponds to the configurable parameters of the primary host computer110. As used herein, the term “configurable parameters” includes information such as the IP or other network address(es) of the primary host computer110, the node name of the primary host computer110, the domain name of the primary host computer110, and any other relevant information of the primary host computer110that is unique to the primary host computer110and used to identify and allow access to the primary host computer110over the communication network to which it is attached (i.e., network140). Typically these configurable parameters are saved in a configuration database that is accessed by the operating system of the primary host computer110and is stored on storage system130.

When the data of the primary host computer110is replicated to storage system130′ for use by the secondary host computer120, the replicated data will include the configurable parameters of the primary host computer110. However, the use of the configurable parameters of the primary host computer110by the secondary host computer120may prevent access to the secondary host computer120. This is because the primary and secondary host computers110,120are located in different networks, and most bridges or routers filter or forward packets according to their destination IP or other network address. Thus, were the secondary host computer to keep the configurable parameters of the primary host computer110, any communications originating outside network140′ and directed to the IP or other network address of the primary host computer110may not be routed or forwarded to network140′.

To permit access to the secondary host computer120that is in a different LAN than the primary host computer110, the configurable parameters of the primary host computer110are modified at step634to a value that is valid and not already in use in network140′. For example, where the secondary host computer120already has an IP or other network address, node name, domain name, etc. that is valid in network140′ (e.g., prior to the secondary host computer120being shutdown in step622), the configurable parameters of the primary host computer110may be modified to those prior values. This may be performed, for example, by saving configurable parameters of the secondary host computer120in a memory of the controller160, or elsewhere, prior to step630. After replication, the replicated data corresponding to the configurable parameters of the primary host computer110can then be modified by the controller160to reflect those of the secondary host computer120.

In one embodiment of the present invention, the replicated data corresponding to the configurable parameters of the primary host computer110are directly modified by the controller160to a value that is valid on network140′. This direct modification may be performed by understanding where this information is stored within the operating system of the primary host computer110. For example, by comparing the data of the primary host computer110that is stored on storage system130when the configurable parameters of the primary host computer110have a first value to the data of the primary host computer110that is stored on storage system130when the configurable parameters of the primary host computer110have a second value, the location of where and how these configurable parameters are stored can be determined. By instructing the controller160to change the appropriate bits to a new value, the configurable parameters may thus be directly modified. However, as described further below, other methods may alternatively be used to modify the configurable parameters of the primary host computer, as the present invention is not limited to a particular method.

After modifying the configurable parameters of the secondary host computer120, the routine proceeds to step640, wherein the secondary host computer120is either manually or automatically powered on and brought on line as a replacement to the primary host computer110. After bringing the secondary host computer120on line, the routine proceeds to step650, wherein the controller160modifies the network director515to redirect any communications directed to the primary host computer110to secondary host computer120. This may be performed in a well known manner by providing the network director515with the IP or other network addresses of the primary and secondary host computers110,120and instructing the network director515to redirect all communications to the IP or other network address of the primary host computer110to the IP or other network address of the secondary host computer120. From this point onward, any communications directed to the primary host computer110will be automatically redirected to the secondary host computer120. Indeed, because most users request access to host computer systems by node or host name, most users will be unaware that that they are actually access ing a different host computer on a different network than the primary host computer110. After modifying the network director515, the site failover routine terminates.

It should be appreciated that the flowchart ofFIG. 6is but one example of a site failover routine that may be used with the computer environment ofFIG. 5, and that many variations and modifications are possible. For example, where the primary host computer110fails in a manner in which it is not shutdown in an orderly fashion resulting in a loss of data, the data that is replicated at step630may be copied from a backup copy of the data of the primary host computer110, in a manner similar to that described above with respect to FIG.2A. Moreover, it is not required that the data of the secondary host computer120be mirrored, as the data of the secondary host computer120may be backed up prior to replication in step630, or not backed up at all. It should further be appreciated that the replicated data corresponding to the configurable parameters of the primary host computer110need not be directly modified by the controller160, as they may be modified indirectly. For example, after replicating the data of the primary host computer110in step630, the secondary host computer120may be powered on and brought to a stand alone mode. In this standalone mode, the secondary host computer120can be dynamically reconfigured in a well known manner to use different configurable parameters. The secondary host computer120can then be either brought on line with those the new configurable parameters or rebooted and brought on-line.

Further, although the site failover routine described with respect toFIG. 6included a step of modifying the data of the primary host computer110that was replicated to storage system130′, it should be appreciated that the appropriate modifications may be performed at other times. For example, the configurable parameters of the primary host computer110may be changed while that data is still stored on storage system130, prior to any data replication, or alternatively, the configurable parameters of the primary host computer110may be modified during the replication process. Other modifications similar to those discussed with respect to the site failover routines ofFIGS. 2A-C, andFIG. 4may also be performed.

AlthoughFIGS. 1-6were described above in terms of identically configured primary and secondary host computers, the present invention is not so limited. In particular, embodiments of the present invention can also be used to provide renewable host resources for a primary host computer where the renewable host resources are not identical in hardware and/or software to the primary host computer. For example, the primary host computer may be a Windows NT system running an SQL database, whereas the secondary host computer may be a UNIX workstation capable of supporting an ORACLE database. Alternatively, the primary and secondary host computers may run the same type of operating system (e.g., UNIX) and application programs (e.g., ORACLE), but may differ in terms of hardware. For example, the primary host computer may be a multi-processor system, whereas the secondary host computer may include only a single processor. This aspect of the present invention is now described with respect to FIG.7.

As shown inFIG. 7, networked computing environment700includes a primary host computer710and a secondary host computer720that are coupled to a communication network140and a storage system130. One, or both of the host computers710,720may also be coupled to a respective relay170,171, as shown. Networked computing environment700also includes a controller760that is operatively coupled to the primary host computer710, the secondary host computer720, the storage system130, and the relays170,171. However, in contrast to the networked computing environment ofFIG. 1, the primary host computer710and the secondary host computer720need not be identical. In this regard, the primary and secondary host computers710,720may differ in hardware, in software, or both.

To account for differences between the primary and secondary host computers710,720, controller760includes a transformation engine765that transforms data used by the primary host computer710into a format that can be used by the secondary host computer720. Transformation engine765accesses information identifying the configuration (hardware and software) of the primary and secondary host computers710,720and uses this information to determine what changes, if any, should be made to the data of the primary host computer710to allow that data to be used by the secondary host computer720. Data of the primary host computer710that may be changed by the transformation engine765can include the data forming an application program or programs, application program data (i.e., the data accessed by one or more application programs), and even data that is accessed by the operating system, such as device drivers for network interface cards, communication adapters, etc.

As in the previously described controller160ofFIG. 1, when a change in the operational status of the primary host computer710is detected by the controller760, the controller760determines whether the operational status of the secondary host computer720should be modified to provide additional host resources to complement or replace those provided by the primary host computer710. When the controller760determines that additional host resources are to be added, controller760automatically alters the operational status of the secondary host computer720to provide these additional resources. However, when the configuration of the primary host computer710differs from that of the secondary host computer720, controller760also instructs the transformation engine765to make changes to the data of the primary host computer710to allow that data to be used by the secondary host computer720.

In one embodiment of the present invention, controller760copies relevant data of the primary host computer710that is stored on storage device(s)135of storage system130, instructs the transformation engine765to transform the relevant data to allow operation on the secondary host computer720, and copies the transformed data to other storage locations that can be accessed by the secondary host computer720. In a manner similar to that described with respect to FIGS.1and2A-2C, the transformed data may be copied to a different storage device135of storage system130than that used by the primary host computer710, or alternatively, the transformed data may be copied to a different storage system (e.g., storage system130′ in FIGS.3and5), in the same network or in a different network, than that used by the primary host computer710in a manner similar to that described with respect toFIGS. 3-6. Once the relevant data has been copied and transformed, the secondary host computer720can be brought on line to provide these additional host resources.

Operation of one embodiment of the present invention that is directed to a site failover is now described with respect to FIG.8. Advantageously, this embodiment permits a secondary host computer720to be configured and brought on line to replace a primary host computer710, even when the primary and secondary host computers710,720are not identical. Although the operation of the site failover routine is now described in connection with a single storage system (i.e., storage system130), it should be appreciated that it may also be used with multiple storage systems located in the same or different networks in a manner similar to that described above with respect toFIGS. 3-6. Moreover, although the site failover routine ofFIG. 8is described in terms of a secondary host computer720that maintains a mirror copy of its data and is located in the same LAN as the primary host computer710, the present invention is not so limited, as described further below.

At step805, the site failover routine identifies the configuration of the primary host computer710and saves this information. The information that is saved may include software related information identifying software that is used by the primary host computer710(such as the operating system (e.g., Solaris, SunOS, AIX, etc.), and its version used by the primary host computer710, any application programs (e.g., Word, PageMaker, etc.), and their versions, used by the primary host computer710, etc); hardware related information, such as the number and type of processors used by the primary host computer710, the type (and revision level) of I/O or network controllers used by the primary host computer710; as well as any of the configurable parameters of the primary host computer710, such as the IP or other network address(es) of the primary host computer710, its node name, its domain name, and other relevant information of the primary host computer710that is used to identify and allow access to the primary host computer710. This information may be saved in any location accessible by the controller760and the transformation engine765, such as a memory of the controller760, a memory of the storage system130, or in a storage device135of the storage system. In one embodiment of the present invention, where both the controller760and the transformation engine765are implemented in software executing on the storage processor133of the storage system, the configuration identification information is stored in the storage system130. It should be appreciated that the configuration identification information that is saved at step805may be saved at any time after the primary host computer710is booted and on-line, and may updated whenever that configuration information changes, for example, when new software or hardware is added or removed.

After saving the configuration of the primary host computer710, the site failover routine proceeds to step807, wherein the site failover routine saves configuration identification information relating to the secondary host computer720in a manner similar to that of step805. It should be appreciated that the configuration identification information of the secondary host computer720that is saved at step807may be saved at any time prior to the reconfiguration of the secondary host computer720as a replacement for the primary host computer710. Moreover, this step of saving information identifying the configuration of the secondary host computer720may be executed more than once, whenever the configuration of secondary host computer720changes.

After saving information identifying the configuration of the primary and secondary host computers710,720, the site failover routine proceeds to step810, wherein the failover routine awaits the detection of a malfunction or failure of the primary host computer710. As described above with respect toFIGS. 1-6, this may be detected in any number of ways, such as by being informed by an agent (e.g., agent162inFIG. 1) of the primary host computer710that a failure was detected or is imminent, by not receiving a status message from the agent within a particular time interval, by the controller760actively querying the primary host computer710as to its status, or by a combination of any of the above techniques. When it is determined at step810that no failure, imminent failure, or other malfunction has been detected, the failover routine waits at step810. When a failure, imminent failure, or other malfunction that impairs the operation of the primary host computer710is detected at step810, the routine proceeds to step820.

At step820, the controller760performs an orderly shutdown of the primary host computer710, if possible, and then proceeds to step822. As noted previously, an orderly shutdown of the primary host computer710helps to ensure that the primary host computer710is no longer active on the network, and will generally cause any outstanding changes to data that is to be stored in the storage system130to be flushed from the primary host computer710, so30that the data of the primary host computer710that is stored in storage system130is current. When an orderly shutdown of the primary host computer710is not possible, or in addition to performing an orderly shutdown of the primary host computer710, the controller760may also issue a command to instruct relay170to turn off power to the primary host computer710, thereby ensuring it is no longer an active participant on the network.

At step822, the controller760shuts down the secondary host computer720in a manner similar to that described with respect toFIG. 2C, wherein the routine proceeds to step824. At step824, the controller760issues an instruction to the storage system130to break or discontinue the mirroring of the data of the secondary host computer720in a manner similar to that described with respect to FIG.2C. After instructing the storage system130to discontinue the mirroring of data, the routine proceeds to step826, wherein power to the secondary host computer is turned off. As noted with respect toFIG. 2C, this step may be performed automatically by issuing a command to relay171, or alternatively, may be performed manually. After shutting off power to the secondary host computer720, the site failover routine proceeds to step828.

At step828the controller760determines whether the configuration of the primary and secondary host computers710,720is identical. As should be appreciated by those skilled in the art, strict identity of the primary and secondary host computers710,720is not necessary. That is, some differences between the primary and secondary host computers710,720, such as the clock speed at which the processors of the host computers operate, may not require any data transformation to operate on both the primary and secondary host computers710,720. As will be described further below, whether any changes should be made to the data of the primary host computer710to allow operation on the secondary host computer720, and what those changes are, can be determined by actual experimentation. Once those changes are identified, a transformation routine can be provided to allow the transformation engine765to perform the necessary changes.

When it is determined at step828that the primary and secondary host computers710,720are identical, such that no transformation of data is necessary, the routine proceeds directly to step830. At step830, the data of the primary host computer720is replicated or copied to the one or more storage devices135that are accessible to the secondary host computer720and on which the primary copy of the data of the secondary host computer720was previously stored. In one embodiment, the data that is replicated at step830includes the operating system, as wells as any application programs and application program data of the primary host computer710. Although this step of replicating the data of the primary host computer710overwrites the primary copy of the data that was previously used by the secondary host computer720, the mirrored copy is not affected. After replicating the data of the primary host computer710, the secondary host computer720is either manually or automatically powered on and brought on line as an identical replacement to the primary host computer710in a manner similar to that described above with respect toFIG. 2C, wherein the routine terminates.

Alternatively, when it is determined at step828that the primary and secondary host computers are not identical and data transformation is required to allow operation on the secondary host computer720, the routine proceeds to step835. At step835, the site failover routine copies and transforms any relevant data of the primary host computer710that is needed for use on the secondary host computer720. The copied and transformed data is stored in the one or more storage devices135that are accessible to the secondary host computer720and on which the primary copy of the data of the secondary host computer720was previously stored. The data that is transformed and copied may include application program data, application programs, and even data that is accessed by the operating system, or portions of the operating system of the primary host computer710. For example, where the primary and secondary host computers710,720differ in hardware, but are both SUN workstations running the Solaris operating system version 2.5.1 or 2.6 and using ORACLE 7.3.4 database software, the data that is transformed and copied can include the operating system, the application program (e.g., the executable image of the application program) and the application program data. Only minimal changes are required to use the operating system data and the application program data of the primary host computer710on a differently configured secondary host computer720, and no changes to the application program data are needed. It should be appreciated that what type of data (operating system data, application programs, or application program data) is transformed and copied at step835will depend upon the nature and extent of differences between the primary and secondary host computers710,720, as described further below. After transforming and copying the data at step835, the routine proceeds to step845as described above, after which the routine terminates.

Advantageously, the site failover routine ofFIG. 8permits both the primary and secondary host computers710,720to be fully operational prior to a detected failure of the primary host computer710. In this regard, the primary and secondary host computers710,720may both be active in the same, or in different networks, each with their own unique identity. It should be appreciated that when the primary and secondary host computers710,720are located in different networks (e.g., FIG.5), the site failover routine ofFIG. 8may be modified to permit access to the secondary host computer720from other networks. For example, after step830, the data corresponding to the configurable parameters of the primary host computer710that was replicated at step828or replicated and transformed at step835may be modified to any value that is valid in the communication network in which the secondary host computer720is located. By saving the configuration information of the secondary host computer720at step807, the configurable parameters of the secondary host computer may be reset to their prior value.

Other modifications and variations to the site failover routine may also be performed in a manner similar to those described above with respect to the site failover routine ofFIGS. 2A-2C,4, and6. For example, when the primary host computer710fails in a manner in which it cannot be not shutdown in an orderly fashion, and data is lost, the controller760can be provided with a location of where the most recent backup copy of the data of the primary host computer710is stored, and can utilize that backup copy of data. As noted previously, the location of the most recent copy of backup data of the primary host computer710can be provided to the controller760prior to failure, so that manual intervention is not necessary. The backup copy may be resident on other storage devices135of the storage system130, or may be copied from another storage system for this purpose. Once the backup data is obtained, any necessary translation of data may be performed as described above.

As noted above, the type of data that is copied from the primary host computer710and the nature and extent of any transformation of that data necessary to permit operation on the secondary host computer720will vary depending upon differences between the primary and secondary host computers710,720. Identifying what changes, if any, should be made to the data of the primary host computer710to allow operation on the secondary host computer720can be determined by actual experimentation. For example, by configuring the secondary host computer720with the same operating system, application programs and application program data as that used by the primary host computer710, one can then compare the data used by each host computer. Any differences that are found can then be attributed to differences in the hardware of the primary and secondary host computers710,720. Where those differences are relatively few in number, the transformation engine765can then modify those portions of the data necessary to permit operation on the other host computer.

Alternatively, where the differences are greater in number, further analysis may be necessary to identify whether the differences are related to the operating system, the application programs, the application program data, or all of the above. Depending on where those differences are located (operating system, application programs, or application program data), only certain data may be copied (or copied and transformed) for use by the secondary host computer720. For example, if significant differences are present between the data used by the primary host computer710and that used by the secondary host computer720, but these differences are substantially limited to the operating system, the application programs and application program data of the primary host computer710may be capable of use on the secondary host computer720with little or no modification. An example of this situation is where the primary host computer710has only a single processor and the secondary host computer720has multiple processors, but both are capable of running the same type of operating system (e.g., Solaris) and application programs (e.g., ORACLE). In this example, the site failover routine ofFIG. 8may be modified to use the existing operating system of the secondary host computer720and copy (or transform and copy) only that data from the primary host computer710that relates to application programs and application data. This may be facilitated by storing the operating systems of the primary and secondary host computers710,720on a different storage device135or storage volume than application programs and application program data.

Alternatively, an analysis of the differences between the data used by the primary host computer710and that used by the secondary host computer720may reveal that significant differences are present in both the operating system and the application programs (i.e., the executable images of the application programs) used by the primary and secondary host computers710,720, but not the application program data. Indeed, Applicants have found that despite significant differences in hardware between primary and secondary host computers, and despite significant differences between the operating systems and application programs of the primary and secondary host computers, the application data used by the same type of application program is frequently similar between two very different host computers. Where the application program data is similar, only this data can be replicated for use on the secondary or failover host computer. This is significant, because it is the application program data that is typically of most importance to users. Thus, where the application program data is sufficiently similar between the primary and secondary host computers, the site failover routine ofFIG. 8may be modified to use the existing operating system and application programs of the secondary host computer, and copy (or transform and copy) only the application program data from the primary host computer. Indeed, empirical testing has demonstrated that embodiments of the present invention may be used to transform ORACLE database application program data used by a SUN Solaris system for use with an ORACLE database application program on a Windows NT system, with only minor transformations needed to account for differences in file format.

According to a further embodiment of the present invention, a site failover routine is now described to provide site failover for a host computer that supports a database. This embodiment can be used to provide site failover for a primary host computer in which the secondary or failover host computer differs in terms of both hardware and software from the primary host computer. Although this embodiment is described in terms of a primary host computer that includes a SUN workstation running ORACLE version 7.3.4 database software on the Solaris to operating system, and a secondary host computer that includes an Intel Pentium-based server running SQL version 6.5 database software on a Windows NT operating system, it may readily be adapted to provide site failover for other computing environments. Further, although this embodiment is described with respect to primary and secondary host computers connected to a single storage system on the same network (e.g., computing environment700of FIG.7), it should be appreciated that it may readily be modified for use with host computers connected to different storage systems on the same network, and with host computers connected to different storage systems on different networks. Operation of this exemplary embodiment is now described with respect to the flow diagram of FIG.9.

At step910, the site failover routine identifies the configuration of the primary and secondary host computers710,720and saves this configuration identification information. In a manner similar to that described with respect toFIG. 8, the information that is saved may include identifiers of the type and version of the operating system used by the primary and secondary host computers710,720, identifiers of application programs and their versions, the number and type of processors used by the host computers, the type and revision level of I/O or network controllers, and any of the configurable parameters of the host computers, such as their IP or other network address(es), their node name, their domain name, and other relevant information of the primary and secondary host computers710,720that is used to identify and allow access to the host computers. This configuration information may be saved in any location accessible by the controller760and the transformation engine765, such as a memory of the controller760, a memory of the storage system130, or in a storage device135of the storage system.

After saving the information identifying the configuration of the primary and secondary host computers710,720, the site failover routine proceeds to step915, wherein the controller760replicates and transforms the application program data used by the primary host computer710to permit use by the secondary host computer720. In one embodiment, this step is facilitated by storing application program data of the primary host computer710in a location that is different from that of the operating system and application programs of the primary host computer710(e.g., in a different storage device135of the storage system than that used to store the operating system and application programs used by the primary host computer710). The controller760locates and copies the application program data from the storage device135on which it is stored (or alternatively from a mirror of that storage device), transforms that application program data for use on the secondary host computer720, and copies the transformed application data to another location (e.g., a different storage device135) of the storage system130that can be accessed by the secondary host computer720. Transformations that may be made to the application data can include modifying the file format in which the application program data is stored, modifying the data format (e.g., high order bit first, or high order bit last), etc. Those transformations that are necessary to permit use by the secondary host computer720can again be determined in advance, by entering the same application program data on different systems, and comparing the manner in which that data is stored by each application program. Once those differences are ascertained, the transformation engine765can be configured, in advance, to perform the necessary modifications.

After replicating and transforming the application program data, the routine proceeds to step920, wherein the failover routine awaits the detection of a malfunction or failure of the primary host computer710. The malfunction or failure of the primary host computer710may be detected in any number of ways, as described above with respect toFIGS. 1-8. When it is determined that no failure, imminent failure, or other malfunction has been detected, the failover routine waits at step920. Alternatively, when a failure, imminent failure, or other malfunction that impairs the operation of the primary host computer710is detected at step920, the routine proceeds to step925.

At step925, the controller760performs an orderly shutdown of the primary host computer710, where possible, in a manner similar to that described previously with respect toFIGS. 1-8. As in the previously described embodiments, power to the primary host computer710may also be turned off either manually or automatically. After shutting down the primary host computer710, the site failover routine proceeds to step930. At step930, the controller760locates, copies, and transforms the transaction log file of the application program on the primary host computer710to permit it to be applied to the transformed data that was replicated and transformed at step915. The copied and transformed transaction log file may be temporarily stored in a memory of the controller760, or a storage location in the storage system. The copied transaction log file for the database on the primary host computer710is modified so that the transformed data intended for use by the secondary host computer720can be updated to reflect any changes made since the application program data was replicated and transformed at step915. Identifying what modifications are to be made to the copied transaction log file in step930can be determined in advance, based upon a knowledge of how application program data is stored, and how the transactions are logged, by each application program. For example, by comparing the same application program data entered into different databases on the primary and secondary host computers710,720and analyzing how that data is stored by each database, the correspondence of how data is organized and stored by each database can be determined. By then changing data in each database and analyzing how that transaction is logged by each transaction log file, one can identify the correspondence between the transaction log file on the primary host computer710and that of the secondary host computer720. Once it is determined how the transaction log file for the database application on the primary host computer710corresponds to that of the database application on the secondary host computer, the controller760may be configured, in advance of a failure of the primary host computer710, to perform the necessary modifications during execution of the site failover routine. After transforming the transaction log at step930, the routine proceeds to step935.

At step935, the transaction log file that was transformed at step930is applied to the transformed application program data that is to be used by the secondary host computer720. This updates the application program data that will be used by the secondary host computer720to be as current as that on the primary host computer710when the failure occurred and the primary host computer was shut down. After applying the transaction log to the transformed data, the routine proceeds to step940.

At step940the controller760modifies the configurable parameters of the secondary host computer720to be identical to those of the primary host computer710. As discussed previously with respect toFIG. 6, this step may be performed when the secondary host computer720is in a stand alone state, but off-line. After configuring the secondary host computer720as a replacement to the primary host computer710, the routine proceeds to step945, wherein the secondary host computer720is brought on line as replacement to the primary host computer710, and the routine terminates.

It should be appreciated that although the exemplary site failover routine ofFIG. 9included a step of transforming the transaction log file of the application program on the primary host computer710into a form that can be applied to the secondary host computer720, the present invention is not so limited. For example, some application programs permit data files and/or transaction log files to be exported and imported in an application independent format. Where the database or other applications executing on the primary and secondary host computers710,720support the exporting and importing in an application independent format, the application data or transaction log file may be exported from the primary host computer710and saved in an application independent format. The application program or transaction log file data can then be imported by the secondary host computer720for use by the application program and applied to the replicated data in a well known manner.

Although embodiments of the present invention have been described in terms of individual host computers (e.g., primary and secondary host computers110,120of FIG.1), the present invention is not so limited. In particular, it should be appreciated that each host computer described with respect toFIGS. 1,3,5, and7may include a plurality of host computers that together form a computing site. For example,FIG. 10illustrates a networked computing environment in which renewable host resources may be provided for computing sites that include multiple host computers.

As shown inFIG. 10, primary computer site1010includes two host computers1011and1012, secondary computer site1020includes three host computers1021,1022, and1023, and tertiary computer site1030includes a single host computer1031. Each of these computer sites is coupled to a communication network140. Each of these computer sites is also coupled to one or more storage systems130,130′ and to a controller1060by a network140′. The controller1060may be operatively coupled to a number of relays (not shown) that are capable of providing or shutting off power to a respective computer site, or to individual computer within a respective computer site. Controller1060is capable of providing renewable host resources for one or more of the host computer sites, and may include a transformation engine1065for transforming data for use by different host computers. Network140′ may be the same network or a different network than communication network140. In this regard, all that is necessary is that controller1060be able to communicate with each host computing site1010,1020,1030that is part of the networked computing environment for which renewable resources are to be provided, and, where data is to be replicated to a different storage system (e.g., storage system130′), with each storage system that is involved in the replication of data, by using a point to point connection, such as SCSI or ESCON, or by a network connection, such as Fibre Channel. Moreover, it should be appreciated that the host computer sites1010,1020,1030and the storage systems130,130′ may be located in the same network140, in different networks, and in different geographical locations.

In the exemplary networked computing environment ofFIG. 10, secondary computing site1020may be configured as a failover site for primary computer site1010, tertiary computer site1030, or both. For example, when a failure of the primary computer site1010is detected, controller1060can configure the secondary computer site1020(e.g., host computers1021,1022) as a replacement for the primary computer site1010, shut down the primary computer site1010, and then bring the secondary computer site1020on line as a replacement to the primary computer site1010in the manner discussed above. Alternatively, when a failure of the tertiary computer site1030is detected, controller1060can configure the secondary computer site1020(e.g., host computer1023) as a replacement for the tertiary computer site1030, shut down the tertiary computer site1030, and then bring the secondary computer site1020on line as a replacement to the tertiary computer site1030. Were tertiary computer site1030to fail during the time that site failover was being provided for the primary computer site1010, host computers1021and1022could provide site failover for the primary computer site, while host computer1023was configured to provide site failover for tertiary computer site1030. Assuming that the primary and tertiary computer sites1010,1030were identical to the secondary computer site1020, no transformation of data by the transformation engine1065would be needed. Alternatively, when the primary computer site1010or the tertiary computer site1030is not identical to the secondary computer site1020, and a failure of the primary computer site1010or the tertiary computer site is detected by the controller1060, some data transformation may be needed prior to replacing the primary computer site1010or the tertiary computer site1030.

In a manner similar to that described above with respect toFIGS. 1,3,5, and7, an agent may be provided for each computer site, or for each host computer within a respective for which site failover is desired. For example, as shown inFIG. 10, both primary computer site1010and tertiary computer site1030include a respective agent162,162′. Each agent162,162′ may be implemented in software that executes on a processor of the respective host computer1011,1031to monitor the operation of the computer site and report any errors to the controller1060. When notified by the agent162or162′ that a malfunction affecting the operation of a computer site has been detected, or when a status report has not been received at the appropriate interval, the controller1060shuts down the appropriate site1010,1030and configures the secondary computer site1020to act in its stead. It should be appreciated that an agent can also be provided for each respective host computer within a respective computer site.

The operation of a site failover routine that may be performed by the controller1060ofFIG. 10is similar to that ofFIGS. 2A,2B,4,6,8, and9described above. For example, where the primary computer site1010and the secondary computer site1020are identical and are coupled to the same network (e.g., network140), the site failover routine ofFIGS. 2A-2Cand4may be executed by the controller1060to replace primary computer site1010with secondary computer site1020. Alternatively, where the primary computer site1010and the secondary computer site are not identical, the site failover routine may operate in a manner similar to that discussed above with respect toFIGS. 8 and 9. As the operation of the site failover routine for the networked computing environment1000would be similar to those discussed previously, further detailed explanation of the operation of a site failover routine to be used with the networked computing environment1000ofFIG. 10is omitted.

It should be appreciated that the above described embodiments of the present invention overcome many of the disadvantages of conventional methods of site failover. For example, because a strict identity of host computers is not required, a single host computer or computer site can provide site failover for a number of different host computers or a number of different computer sites. Embodiments of the present invention are also capable of automatically performing site failover in the event of malfunction or failure, and thus dispense with the need for on site personnel to effect site failover. Indeed, no manual intervention by a system administrator or other personnel is required, as the detection of a malfunction or failure in the primary host computer or primary computer site and the subsequent configuration of a failover host computer can be performed automatically by the controller. Furthermore, embodiments of the present invention are virtually transparent to the host computer for which failover is provided, as the host computer is not involved in copying backup data for use in the event of a failure.

Although the present invention has been described in temms of providing site failover for a host computer in which a malfunction or failure is detected, it should be appreciated that site failover is but one example of a renewable host resource. In this regard, embodiments of the present invention may also be used to provide other types of renewable host resources. For example, rather than providing replacement host resources for a primary host computer, embodiments of the present invention may be also used to provide host resources that complement, not replace, the primary host computer.

Thus, according to another aspect of the present invention, a controller is provided that is capable of dynamically configuring another host computer to provide additional computer resources that complement those provided by a primary host computer. In one embodiment, the controller monitors the performance of a primary host computer, and when the controller detects that the performance of the primary host computer is deficient or below a predetermined threshold, the controller automatically configures additional host resources to share in the operational load of the primary host computer. Operation of this aspect of the present invention is now described with respect to the networked computer environment100of FIG.1.

As discussed previously with respect toFIG. 1, controller160is capable of detecting a change in the operational status of the primary host computer110and, in response to that change in operational status, automatically altering the operational status of a secondary host computer120. However, rather than detecting a malfunction or failure of the primary host computer, controller160may alternatively be adapted to detect a diminished performance of the primary host computer10and automatically configure the secondary host computer120to provide additional resources that complement the operation of the primary host computer110.

According to one embodiment of the present invention, controller160periodically queries the primary host computer110to determine its performance. For example, the controller160may query the primary host computer110as to the amount of processor utilization, how much memory is being used, how frequently that memory is being swapped out to disk, how many I/O requests are pending, etc. Alternatively, the controller160may query the primary host computer110for higher level information, such as how many user requests are pending, or how many transactions per unit time are being serviced. Based upon the responses from the primary host computer10to those queries, the controller160can determine whether additional host computing resources should be provided. It should be appreciated that because the performance of a computer system can change significantly from one moment to the next, controller160may monitor the responses from the primary host computer110over time. For example, based upon changes in performance metrics of the primary host computer110over time, the controller160can determine whether those changes are transitory in nature, or are of a more sustained duration. Further, by a comparison of those performance metrics to a predetermined threshold of performance that provides an acceptable response, or by a comparison of those performance metrics to an operational capacity of the primary host computer110, the controller160can determine whether performance is deficient and additional resources should be provided. When it is determined that performance of the primary host computer110is not of a transitory nature and the performance of the primary host computer110is below the predetermined threshold, the controller160can configure the secondary host computer120to share in the load of the primary host computer110.

Alternatively, rather than the controller160periodically querying the primary host computer110as to its performance, an agent may be provided for the primary host computer that monitors its performance. For example, inFIG. 1, agent162may be modified to monitor various performance metrics such as processor utilization, memory utilization, how often memory is swapped out to disk, the number of pending I/O requests, etc., and report those metrics back to the controller160. In one embodiment of the present invention, agent162monitors the performance of the primary host computer110and provides performance metrics to the controller160for analysis. Based upon a review of those metrics over time and a comparison of those metrics to a predetermined threshold, the controller160can determine whether additional host computer resources should be added. Alternatively, in another embodiment, the agent162monitors the performance metrics, compares those metrics over time to a predetermined threshold of performance, and informs the controller160when additional host computer resources should be added.

The performance monitoring of computers is well understood in the art. For example, there are numerous performance monitoring packages that are commercially available for different types of host computers (such as workstations, mainframes, PC's, etc.) and a myriad of operating systems that are capable of reporting a wide variety of performance metrics. Some of these performance monitoring packages measure and monitor performance metrics such as CPU utilization, cache hit rates, I/O utilization, memory utilization, etc. Other commercially available performance monitoring packages measure and monitor higher level information such as the number of transaction requests per unit of time (e.g., transaction requests per second) and the number of transaction requests being serviced per unit of time. Such commercially available performance monitoring packages can be installed and executed on a processor of the primary host computer110and their output periodically monitored by the controller160, or agent162. Alternatively, a dedicated performance monitoring routine may be implemented by the controller160, or agent162that monitors performance in a manner that is similar to that provided by such commercially available monitoring routines. Because embodiments of the present invention are not limited to a particular method of monitoring performance, and because methods of monitoring performance are well understood in the art, further details of how performance can be monitored are omitted herein.

Further, although embodiments of the present invention monitor performance metrics and compare these metrics to a predetermined threshold to determine whether performance is deficient, the present invention is not limited to a particular metric nor a particular predetermined threshold. For example, as is known to those skilled in the art, the level of performance below which a host computer is viewed as deficient will vary based upon a number of factors. These factors include the capabilities of the host computer, the nature of the task being performed, the expectations of users, the cost of the computer services being provided, etc. For example, for a web based application, the predetermined threshold of performance can be based on a number of requests for information (i.e., hits) that can be serviced per second. Alternatively, the predetermined threshold can be based on the amount of time it takes for a request to be serviced. When the number of hits being received within a certain period is more than the amount that can be serviced within that certain period, or when the amount of time it takes to service a request increases beyond an acceptable leyel, it can be determined that additional host resources should be added to improve performance. The predetermined threshold can alternatively be based on the capacity of the host computer. For example, when a host computer reaches approximately 80% of its operational capacity, it can be determined that additional host resources be added to improve performance. Because the predetermined threshold will vary based upon a number of factors, and because the present invention is not limited to a specific performance metric or predetermined threshold, further discussion is omitted herein.

According to another embodiment of the present invention, a dynamic load balancing routine is now described, with respect toFIG. 11, that is capable of detecting a change in the performance in a primary host computer and automatically configuring a secondary host computer to provide additional host resources. Advantageously, this embodiment may be used to provide additional host resources for any of the computer environments described above with respect toFIGS. 1,3,5,7, and10. However, for purposes of illustration, it is assumed that the primary and secondary host computers110,120are identical to one another and are connected to the same storage system130and the same network140, in a manner similar to that shown in FIG.1. Further, it is assumed that the networked computer environment includes a network director, similar to network director515inFIG. 5, that is coupled to the primary and secondary host computers110,120, and the communication network140; and that the secondary host computer120is in a powered off state, prior to configuration.

At step110, the controller160determines whether the performance of the primary host computer110is deficient. As noted above, this may be determined in a number of ways, such as by actively querying the primary host computer as to its performance, by using an agent (e.g., agent162) to monitor and report performance metrics to the controller160, or by being informed by an agent162of the primary host computer110that the performance of the primary host computer10is deficient. As described above, in one embodiment, the performance of the primary host computer110is monitored over time, by the controller160or an agent162of the primary host computer110, and when a sustained decrease in performance is observed over time, the performance of the primary host computer110is viewed as deficient. When it is determined that the performance of the primary host computer110is not deficient, the load balancing routine waits at step110. Alternatively, when it is determined that the performance of the primary host computer110is deficient, the load balancing routine proceeds to step1120.

At step1120, the controller160replicates all of the data of the primary host computer10that is stored on storage system130(including the operating system, application programs, and application program data) and copies this data to another storage location that can be accessed by the secondary host computer120. As in the previously described embodiments directed to site failover, the data of the primary host computer110that is replicated at step1130may be copied to another storage device of the storage system, or to another storage device on a different storage system (e.g., storage device135′ of storage system130′ inFIG. 3) that is accessible by the secondary host computer120.

In one embodiment, for performance reasons, when the data that is replicated at step1120is replicated to the same storage system as that used by the primary host computer110, this data is stored in a different storage device that is serviced by a different port adapter (e.g., port adapter132B inFIG. 1) and different disk adapter than that used to store the data of the primary host computer110. This helps to ensure that data can be quickly accessed by both the primary and secondary host computers110,120, as different storage devices and adapters are involved in the transfers of data for the different host computers. Where the data of the primary host computer110that is to be shared with the secondary host computer120is mirrored data, the mirror copy of that data may be split off for use by the secondary host computer120without requiring any replication of data.

After replicating the data of the primary host computer110, the routine proceeds to step1130, wherein the secondary host computer120is configured to use the data replicated at step1120, if such configuration is necessary. For example, where the secondary host computer120does not already have an IP or other network address, a node name, a domain name, etc., these configurable parameters are set to an appropriate value to allow access to the secondary host computer120and avoid conflict with other host computers. Alternatively, where the secondary host computer120already has an IP or other network address, a node name, a domain name, etc, the configurable parameters may be set to their previous value (i.e., those of the secondary host computer120prior to reconfiguration). After configuring the secondary host computer120, the routine proceeds to step1140, wherein the secondary host computer120is powered on and brought on line as an alternative host resource to the primary host computer110in a manner similar to that described above with respect toFIGS. 2A-2C,4,6, and8. After bringing the secondary host computer120on line as an alternative to the primary host computer110, the routine proceeds to step1150.

At step1150, the controller160modifies the network director (e.g., network director515inFIG. 5) to redirect communications such as service or connection requests from the primary host computer110to the IP or other network address of the secondary host computer120. For example, the network director515may be modified to distribute all new service requests directed to the primary host computer110to the secondary host computer120, or to both the primary host computer110and the secondary host computer120on an alternating basis, etc. After modifying the network director515, the load balancing routine terminates.

It should be appreciated that after modification of the network director515, new users are able to access the secondary host computer120as an alternative to the primary host computer110. Thus, further decreases in performance of the primary host computer110due to additional users are alleviated. Moreover, after configuration of the secondary host computer120, the operation of the primary host computer110may be modified to redirect some of the older users of the primary host computer110(i.e., those users already being serviced by the primary host computer110prior to the configuration of the secondary host computer120) to the secondary host computer120to increase the performance of the primary host computer110to an acceptable level.

It should be appreciated that the load balancing routine described above with respect toFIG. 11is but one example of a load balancing routine, and that many modifications to this routine are possible. For example, it is not required that the secondary host computer120be in a powered off state prior to being reconfigured to provide additional resources, as the load balancing routine may be modified to bring the secondary host computer120from an on-line state to a powered off state. Moreover, where the application programs and application program data of the primary host computer are capable of execution on the secondary host computer120with the operating system of the secondary host computer120, only the application programs and application program data can be replicated, and the secondary host computer120need not be powered off at all. For example, where an application program is capable of execution on each of the operating systems of the primary and secondary host computers110,120without modification, only the application program and the application program data may be replicated at step1120.

In a manner similar to that described with respect toFIG. 3, the primary and secondary host computers110,120each may be connected to a separate storage system (e.g., storage systems130and130′ in FIG.3), and the data of the primary host computer110replicated from one storage system to another. Moreover, in a manner similar to that described with respect toFIG. 5, the primary and secondary host computers110,120may be connected to different networks (e.g., networks140and140′ in FIG.5), and in a manner similar to that described with respect toFIGS. 8-9, the primary and secondary host computers110,120need not be identical. In this regard, the load balancing routine ofFIG. 11may be modified in a manner similar to that described above with respect to the site failover routines ofFIGS. 2A,2B,4,6, and8-9to account for such variations.

As will be appreciated by those skilled in the art, the replication of data for use by the secondary host computer120, and the subsequent use of that replicated data, makes it possible that, over time, the data used by the secondary host computer120will no longer be identical to that used by the primary host computer110. Where it is important that the data used by the primary host computer110and the replicated data used by the secondary host computer120be identical, a synchronization mechanism may be provided to ensure that the data used by the primary host computer110and the secondary host computer120is the same. Such synchronization mechanisms may be storage based (i.e., implemented by the storage processor (e.g., storage processor133inFIG. 1) of the storage system130), or host based (i.e., implemented on the primary and secondary host computers110,120).

Alternatively, there are many applications in which there is no need for data synchronization because the data that is accessed either doesn't change over time, is accessed only in a read mode, or both. In these applications, dynamic load balancing may be used to provide additional host resources and share the same data among different host computers without any need for data synchronization. One example of an application in which dynamic load balancing may be used to provide additional host resources without requiring any data synchronization is an on-line help server. In most help applications, the information that is provided to users requesting help changes only infrequently, typically when new versions of software are introduced. Because the help data that is provided to users is essentially static, this data may be shared among different host computers without any need for synchronization. In this regard, dynamic load balancing may be used to configure one or more additional host computers with the same information as a primary host computer, and then modify the primary host computer to direct all help requests to the additional host computer(s) to reduce the load on the primary host computer.

Another example of an application in which dynamic load balancing may be used to provide additional host resources without requiring data synchronization is electronic commerce. In electronic commerce applications, users connect or log into an electronic commerce site, such as a web site or an auction site, that is provided by a host computer. In most electronic commerce applications, the data that is most frequently accessed, such as product descriptions, prices, etc. is that which changes only infrequently and is typically accessed in a read mode, called browsing.

However, as known to those skilled in the art, a problem that exists with many electronic commerce sites is that their usage changes dramatically at different times of the day, and at different times of the year. For example, the number of users that can be expected to visit a web site of a toy store may be expected to be higher during evening hours (e.g., 5:00 p.m. to 10:00 p.m.) than during other hours of the day (e.g., 10:00 p.m. to 5:00 p.m.). Furthermore, the number of users that can be expected to visit that same web site can be expected to increase dramatically during the Christmas holiday season (e.g., from after Thanksgiving to Christmas day). If the web site of the toy store is designed to handle the number of users that can be expected at the busiest times of the day and year, then that web site will be greatly under-utilized at other times of the day and year. This is a great waste of computing resources. Alternatively, if the web site of the toy store is designed to handle the number of users that can be expected at other times of the day and year, then that web site will be greatly over-utilized at the busiest times. During these busier times, accessing information from that web site may be intolerably slow, and users may go elsewhere.

Advantageously, embodiments of the present invention may be used to dynamically configure and provide additional host resources for an electronic commerce site during periods of heavy usage, and then dynamically remove the additional host resources thereafter. Moreover, embodiments of the present invention may also be used to support a number of different electronic commerce sites and dynamically provide each with additional host resources during periods of heavy usage, while minimizing the collective amount of host resources provided. For example, by pooling the needs of different electronic commerce sites having different periods of heavy usage, embodiments of the present invention can provide virtually unlimited host resources for each electronic commerce site, while minimizing the collective amount of host resources that are provided. These aspects of the present invention are now described with respect toFIGS. 12-13.

As shown inFIG. 12, computer environment1200includes a primary computer site1210that supports an electronic commerce site, such as a web site, an auction site, etc. The primary computer site1210may include one or a plurality of host computers and is coupled to a storage system130and a secondary host computer1220by a network1241. The networked computer environment1200also includes a network director1215that is coupled to network1241and to another network1240, such as the internet. The network director1215is used to route service requests from network1240to the one or more of the host computers of the primary computer site1210that support the electronic commerce site. As users connect or log into the electronic commerce site, the network director1215examines the connection request and routes the connection request to one of the host computers of the primary computer site1210that is capable of servicing the request. In larger electronic commerce sites where the primary host computer site1210includes a number of host computers, the network director1215may forward connection requests to individual host computers on a round robin basis in an effort to balance usage. As known to those skilled in the art, network director1215may be implemented in a combination of hardware and software on a host computer of the primary computer site1210, or alternatively, in a combination of hardware and software on a dedicated processor that is coupled to the primary host computer site1210. As the operation of the network director1215is well understood in the art (a wide variety of network directors are commercially available from Cisco, Arrowpoint, and others), and the invention is not limited to using any particular network director, further details of the network director1215are omitted herein.

As shown inFIG. 12, networked computing environment1200also includes a controller1260that is coupled to the network1241, and thus to the primary computer site1210, the secondary host computer1220, the storage system130and the network director1215. In one embodiment, controller1260monitors the performance of the primary computer site1210, and when a decrease in the performance of the primary computer site1210is detected, the controller1260automatically configures the secondary host computer1220to provide additional resources. In one embodiment, the controller1260monitors the performance of the primary computer site1210over time, and only those decreases in performance that are of a sustained duration result in the configuration of additional host resources. As in previous embodiments of the present invention, controller1260may be implemented in software on a storage processor133of the storage system130, or alternatively, may be implemented separately therefrom.

In an alternative embodiment, an agent1262is provided for the primary computer site1210that executes on a processor of the primary computer site1210and communicates with the controller1260. The agent1262monitors the performance of the primary computer site1210, and when a decrease in the performance of the primary computer site1210is detected, reports this information to the controller1260. In one embodiment, only those decrease in performance that are of a sustained duration are reported to the controller1260. Upon receiving a report that the performance of the primary computer site1210is deficient, the controller1260configures the secondary host computer1220to provide additional resources.

An exemplary flow diagram illustrating one implementation of a load balancing routine that may be performed by the controller1260ofFIG. 12is now described with respect to FIG.13. For purposes of illustration, it is assumed that the primary computer site1210includes only a single host computer which is identical to secondary host computer1220and located in the same network1241. It is also assume that the secondary host computer1220is initially in a powered off state, and is coupled to a power source by a relay (not shown) that can communicate with the controller1260. The relay may be similar to that described above with respect toFIGS. 1,3,5, and7. However, it should be appreciated that the present invention is not limited in this regard, as other configurations may alternatively be used, as described further below.

At step1310, the controller1260identifies data of the primary computer site1210that is stored on storage system130and which can be shared with one or more additional host computers. The data that is identified as shareable includes only that data of the primary computer site1210that may be read and/or executed, but not modified (i.e., written, edited, or deleted). Examples of data that may be read and/or executed includes web pages describing products or product pricing, web pages describing the organization hosting the electronic commerce site, web pages describing job openings, store locations, store hours, etc. After identifying data which may be shared with additional host computers, the load balancing routine proceeds to step1320.

At step1320, the controller1260determines whether the performance of the primary computer site1210is deficient. As noted above, this may be determined in a number of ways, such as by actively querying the primary computer site1210as to its performance, by using an agent1262to monitor and report performance metrics to the controller1260, or by being informed by the agent1262that the performance of the primary computer site1210is deficient.

In one embodiment, the number of connection requests over time is monitored to assess performance. For example, when the controller1260or agent1262determines that the number of connection requests over a predetermined period of time (e.g., one second) is above a predetermined percentage (e.g., 80%) of the primary computer site's capacity for a sustained period of time (e.g., ten minutes), the performance of the primary computer site1210is viewed as deficient. Alternatively, when the controller1260or agent1262determines that the number of connection requests over the predetermined period of time is be low the predetermined percentage, the performance of the primary computer site1210is viewed as sufficient. The sufficiency of the performance of the primary computer site1210may be determined in a variety of different ways, and in one embodiment, any decrease in performance detected in step1320is of a sustained duration. When it is determined that the performance of the primary computer site1210is not deficient, the load balancing routine waits at step1320. When the performance of the primary computer site1210is determined to be deficient, the load balancing routine proceeds to step1330.

At step1330, the controller replicates the data of the primary computer site1210that is stored on storage system130(including the operating system, any application programs and application program data), as well as the data that was identified in step1310, and copies this data to another storage location that is accessible to the secondary host computer1220. As in the previously described embodiment ofFIG. 11, the data of the primary computer site1210that is replicated at step1330may be copied to another storage device of the storage system130, or to another storage device on a different storage system. As noted with respect to the previously described embodiment ofFIG. 11, for performance reasons, when the data that is replicated at step1330is replicated to the same storage system as that used by the primary computer site1210, this data may be stored in a different storage device (e.g., storage device135) that is serviced by a different port adapter (e.g., port adapter132B) and different disk adapter than that used to store the data of the primary computer site1210. It should further be appreciated that where the data of the primary computer site1210that is to be shared with the secondary host computer1220is mirrored data, the mirror copy of that data may be split off for use by the secondary host computer1220without requiring any replication of data.

After replicating the data of the primary computer site1210, the load balancing routine proceeds to step1340, wherein the routine configures the secondary host computer1220to use the data replicated at step1330, if such configuration is necessary. For example, where the secondary host computer1220does not already have an IP or other network address, a node name, a domain name, etc., these configurable parameters are set to an appropriate value to allow access to the secondary host computer1220and avoid conflict with other host computers. Alternatively, where the secondary host computer1220already has an IP or other network address, a node name, a domain name, etc, these values for the configurable parameters may be used. After configuring the secondary host computer1220, the routine proceeds to step1350, wherein the controller1260powers on the secondary host computer1220and brings the secondary host computer1220on line to complement the primary computer site1210. After bringing the secondary host computer1220on line, the routine proceeds to step1360.

At step1360, the controller1260modifies the network director1215to route at least some new connection requests to the secondary host computer1220. To maintain data integrity, the controller1260modifies the network director1215to route only those new connection requests that solicit information from the electronic commerce site that was identified as sharable at step1310, and not those that modify information. This modification can be performed in a well known manner based upon the contents of the connection request itself. Any new connection requests that solicit information not identified as shareable (i.e., information used by the electronic commerce site that may differ, during the period of load balancing, between the primary computer site1210and the secondary host computer1220) or that modify information on the electronic commerce site, such as placing orders, bidding on a product, etc, are left undisturbed, and thus, will continue to be routed only to the primary computer site1210. However, because the vast majority of connection requests to an electronic commerce site are those that solicit information which does not change over time, and do not modify information, the ability to forward those new connection requests to the secondary host computer1220will, over time, significantly reduce the load on the primary computer site1210. In one embodiment, the network director1215is modified to forward every other new connection request that solicits information from the primary computer site1210to the secondary host computer1220, in a round-robin approach. However, it should be appreciated that, depending upon the processing capabilities of the secondary host computer1220, other techniques may be employed to balance the load between the primary computer site1210and the secondary host computer1220. For example, the network director1215may be modified to forward all new connection requests that solicit information to the secondary host computer1220, or every two out of three such new connection requests, etc. After modifying the network director1215, the load balancing routine terminates.

After modification of the network director1215, at least some of the new connection requests that solicit information from the primary computer site1210are automatically redirected to the secondary host computer1220. Those new connection requests that solicit information that may change during the period of load balancing or that modify information on the primary computer site1210are not affected and continue to be serviced by the primary computer site1210. For example, any connection requests that make purchases, affect inventory, etc., are serviced by the primary computer site1210, and are not permitted to be serviced by the secondary host computer1220. As users that were connected to the primary computer site1210log out, and as new connection requests are distributed among the primary computer site1210and the secondary host computer1220, the performance of the electronic commerce site increases.

It should be appreciated that after the secondary host computer1220has been configured and brought on line to share in the load of the primary computer site1210, the controller1260, or agent1262, may continue to monitor performance of the primary computer site1210. For example, if the performance of the primary computer site1210again decreases over a sustained period of time, other host computers may be additionally configured. Alternatively, if the performance of the primary computer site1210increases by a certain amount at some point after the secondary host computer1220is configured, the controller1260or agent can determine that the secondary host computer1220is no longer needed. For example, the controller1260or agent1262can continue to monitor the performance of the primary computer site1210, and when the number of connection requests over a period of time (e.g., one second) is below a predetermined percentage (e.g., 20%) of the primary host computer site's capacity for a sustained duration (e.g., 20 minutes), the controller1260can reconfigure the network director1215to forward all new connection requests only to the primary computer site1210. After any connection requests open on the secondary host computer1220have been serviced, the secondary host computer1220can be brought off-line, or left alone in a pre-configured state for the next time the performance of the primary computer site1210decreases. Alternatively, the secondary host computer may be reconfigured to provide additional host resources for another host computer site.

It should be appreciated that the implementation of the load balancing routine described above with respect toFIG. 13is but one example, and that many modifications to this routine are possible. For example, it is not required that the secondary host computer1220be in a powered off state prior to be reconfigured to provide additional resources, as the load balancing routine may be modified to bring the secondary host computer1220from an on-line state to an off-line state for reconfiguration. Moreover, the primary computer site1210and the secondary host computer1220each may be connected to separate storage systems, and the data of the primary computer site1210replicated from one storage system to another. In addition, the primary computer site1210may be connected to a different network than the secondary host computer1220, and the host computer(s) of the primary computer site1210need not be identical to secondary host computer1220. In this regard, the load balancing routine ofFIG. 13may be modified to address a wide variety of configurations in a manner similar to that of the site failover routines described previously.

It should also be appreciated that in certain computing environments, less than all of the data of the primary host computer may be replicated for use by the secondary host computer. For example, certain application programs, such as those written in HTML5 (Hyper Text Markup Language) for example, are capable of being executed on a wide variety of host computers and operating systems without modification. Where an application program is independent of the host computer and operating system on which it is executed, only the application program and its application program data may be replicated for use by the secondary host computer1220. This may be facilitated by storing the application program and application program data on a separate storage device from that used by the operating system. Advantageously this data may be replicated for use by the secondary host computer without shutting down or powering off the secondary host computer.

As should be appreciated from the above description, the dynamic load balancing routine ofFIG. 13permits additional host resources to added and removed to support the needs of an electronic commerce site. However, it should be appreciated that embodiments of the present invention also may be used to provide additional host resources for a number of different electronic commerce sites, and is not limited to supporting a single electronic commerce site. For example, consider a networked computer environment that includes a plurality of electronic commerce sites, each having different periods of heavy usage. One electronic commerce site may be web site for a toy store that is typically busiest around the Christmas holiday season, another may be a web site of a fireworks distributor that is typically busiest around the fourth of July, while a third may be a web site of an automobile dealership that is typically busiest around President's day. If each of these electronic commerce sites was configured with sufficient host resources to meet usage requirements during their busiest periods of the year, then a great deal of host resources would be wasted at other times of the year. Alternatively, if each of the electronic commerce sites was configured to meet usage requirements during other times of the year, then each of the electronic commerce sites could potentially lose customers during its busiest time of the year due to inadequate performance.

Embodiments of the present invention may be used to dynamically configure a plurality of electronic commerce sites with additional host resources necessary to meet usage requirements during their busiest periods, while using these additional host resources elsewhere during other times. Indeed, by servicing the needs of different electronic commerce sites, each with varying periods of heavy usage, each electronic commerce site can be provided with additional host resources during periods of heavy usage, while minimizing the collective amount of host resources provided. It should be appreciated that because embodiments of the present invention may be used in a wide variety of network topologies, there is no requirement that each of the different electronic commerce sites, each of the storage systems involved in the replication of data (where multiple storage systems are involved), or the controller, be present in the same geographic location or located in the same Local Area Network (LAN). Further, only a single controller (e.g., controller1260) need be used to provide each of the plurality of electronic commerce sites with additional host resources. In addition, where the controller is implemented on a storage processor of a storage system, little additional hardware is required to provide nearly unlimited host resources for each electronic commerce site. It should appreciated that where an electronic commerce site is implemented using an application programming language that is host and operating system independent, one or more host computers can service the demands of a number of electronic commerce sites implemented on a number of different host computer/operating system platforms.

According to a further aspect of the present invention, embodiments of the present invention that are directed to dynamic load balancing may be combined with the previously described embodiments directed to site failover. In this regard, a first controller can be configured to provide site failover, while a second controller can be configured to provide dynamic load balancing. Alternatively, both features may be combined in a single controller that may be implemented by a storage processor of a storage system. As should be appreciated by those skilled in the art, the ability to provide either site failover, load balancing, or both, in a manner that is transparent to a host computer, opens up a number of business opportunities that were not previously possible. For example, rather than a business providing for all of their computer needs in house, the business can purchase a number of inexpensive client processors that connect via a network to the host computers and storage systems of an outside service provider. For example, inFIG. 10, each of the client processors of a first business may connect via network140to the primary computer site1010of an outside service provider, and each of the client processors of a second business may connect via network140to the tertiary computer site1030of the outside service provider. Data storage, site failover, and dynamic load balancing for each business may be provided by the outside service provider using secondary computer site1020, controller1060, and storage systems130and130′ in a manner similar to that described above with respect toFIGS. 1-13. By pooling the requirements of several such businesses, the outside service provider can provide non-interruptible and virtually unlimited host resources for each business. Moreover, each business is spared the expense of having additional host resources to meet their demands, while the outside service provider can share the expense of providing such additional resources over a number of different businesses.