Processing input/output requests using proxy and owner storage systems

Methods, apparatus and computer program products implement embodiments of the present invention that include configuring a first storage system as a proxy for a logical volume stored on a second storage system. The first computer system receives an I/O request from a host computer for the logical volume, the host computer, and identifies a port on the second storage system for the I/O request. In some embodiments, the second storage system has multiple SCSI ports, and the identified port comprises a least busy SCSI port. A probe request verifying availability of the logical volume is conveyed to the identified port, and upon receiving a response from the second storage system verifying the availability of the logical volume for the I/O request, the I/O request is conveyed to the identified port, a result of the I/O request is received from the identified port, the result is conveyed to the host computer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Patent Applications titled “Load Balancing Input/Output Operations Between Two Computers”, “Impersonating SCSI Ports Via an Intermediate Proxy”, “Safely Mapping and Unmapping of Host SCSI Volumes”, “Unit Attention Processing in Proxy and Owner Storage Systems” and “Online Migration of a Logical Volume Between Storage Systems” filed on even date with the present application, and which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to storage systems, and specifically to a storage facility configured to process input/output requests via a proxy storage system.

BACKGROUND

In a storage area network (SAN), remote computer storage devices such as disk arrays can be made accessible to host computers so that the storage devices appear as if they are locally attached to the host computer's operating system. SANs may be implemented using Small Computer System Interface (SCSI) storage devices, in which SCSI protocol entities perform input/output (I/O) operations (e.g., data reads and writes) and are exposed through a unique identifier such as a logical unit number (LUN) on a path. A given LUN typically corresponds to a logical volume, and may be represented within the host computer's operating system as a device. Interaction with a LUN is initiated by a SCSI initiator port on a host computer, which can issue various I/O request types to the LUN on a target data storage device.

SUMMARY

There is provided, in accordance with an embodiment of the present invention a method, including configuring a first storage system as a proxy for a logical volume stored on a second storage system, receiving, by the first storage system, an input/output (I/O) request from a host computer for the logical volume, the host computer, identifying a port on the second storage system for the I/O request, conveying, to the identified port, a probe request to verify an availability of the logical volume for the I/O request, and upon receiving a response from the second storage system verifying the availability of the logical volume for the I/O request, conveying the I/O request to the identified port, receiving a result of the I/O request from the identified port, and conveying the result to the host computer.

There is also provided, in accordance with an embodiment of the present invention a proxy storage system, including a proxy port coupled to a storage area network (SAN), and a processor configured to receive an input/output (I/O) request from a host computer for a logical volume, the logical volume mapped between the host computer and the proxy storage system, to identify an owner port on an owner storage system for the I/O request, the owner storage system storing the logical volume, to convey, to the identified owner port, a probe request to verify an availability of the logical volume for the I/O request, and upon receiving, via the proxy port, a response from the owner storage system confirming the availability of the logical volume for the I/O request, to convey the I/O request to the identified owner port, to receive a result of the I/O request from the identified owner port, and to convey the result to the host computer.

There is further provided, in accordance with an embodiment of the present invention an owner storage system, including a storage device configured to store a logical volume, multiple ports configured to communicate with a proxy storage system via a storage area network (SAN), and a processor configured, to receive, via one of the ports, a probe request from the proxy storage system to verify an availability of the logical volume for an input/output (I/O) request from a host computer in communication with the proxy storage system, the logical volume being mapped between the host computer and the proxy storage system, to verify the availability of the logical volume for the I/O request, and subsequent to conveying a response to the proxy storage system confirming the availability of the logical volume for the I/O request, to receive the I/O request from the proxy storage system via the one of the ports, to process the I/O request, and to convey a result of the I/O request to the proxy storage system via the one of the ports.

DETAILED DESCRIPTION OF EMBODIMENTS

There may be instances when a storage administrator wants to migrate the logical volume from a first storage system to a second storage system in order to balance the storage utilization across the storage systems. Embodiments of the present invention provide methods and mechanisms for seamlessly migrating the logical volume from the first storage system to the second storage system. As explained hereinbelow, after copying the logical volume to the second storage system, the first storage system can be configured as a proxy for the logical volume that is now stored on the second storage system, thereby enabling the first storage system to continue to receive and process input/output (I/O) requests for the logical volume. In embodiments described herein the first storage system may also be referred to as a proxy storage controller and the second storage controller may also be referred to as an owner storage controller, wherein the proxy and the owner storage controllers comprise Small Computer System Interface (SCSI) based storage systems that communicate over a multipath Small Computer System Interface (SCSI) based storage area network (SAN).

FIG. 1is a block diagram that schematically illustrates a data processing storage subsystem20, in accordance with an embodiment of the invention. The particular subsystem (also referred to herein as a storage system) shown inFIG. 1is presented to facilitate an explanation of the invention. However, as the skilled artisan will appreciate, the invention can be practiced using other computing environments, such as other storage subsystems with diverse architectures and capabilities.

Storage subsystem20receives, from one or more host computers22, input/output (I/O) requests, which are commands to read or write data at logical addresses on logical volumes. Any number of host computers22are coupled to storage subsystem20by any means known in the art, for example, using a network. Herein, by way of example, host computers22and storage subsystem20are assumed to be coupled by a Storage Area Network (SAN)26incorporating data connections24and Host Bus Adapters (HBAs)28. The logical addresses specify a range of data blocks within a logical volume, each block herein being assumed by way of example to contain 512 bytes. For example, a 10 KB data record used in a data processing application on a given host computer22would require 20 blocks, which the given host computer might specify as being stored at a logical address comprising blocks 1,000 through 1,019 of a logical volume. Storage subsystem20may operate in, or as, a SAN system.

Storage subsystem20comprises a clustered storage controller34coupled between SAN26and a private network46using data connections30and44, respectively, and incorporating adapters32and42, again respectively. In some configurations, adapters32and42may comprise host bus adapters (HBAs). Clustered storage controller34implements clusters of storage modules36, each of which includes an interface38(in communication between adapters32and42), and a cache40. Each storage module36is responsible for a number of storage devices50by way of a data connection48as shown.

As described previously, each storage module36further comprises a given cache40. However, it will be appreciated that the number of caches40used in storage subsystem20and in conjunction with clustered storage controller34may be any convenient number. While all caches40in storage subsystem20may operate in substantially the same manner and comprise substantially similar elements, this is not a requirement. Each of the caches40may be approximately equal in size and is assumed to be coupled, by way of example, in a one-to-one correspondence with a set of physical storage devices50, which may comprise disks. In one embodiment, physical storage devices may comprise such disks. Those skilled in the art will be able to adapt the description herein to caches of different sizes.

Each set of storage devices50comprises multiple slow and/or fast access time mass storage devices, herein below assumed to be multiple hard disks.FIG. 1shows caches40coupled to respective sets of storage devices50. In some configurations, the sets of storage devices50comprise one or more hard disks, which can have different performance characteristics. In response to an I/O command, a given cache40, by way of example, may read or write data at addressable physical locations of a given storage device50. In the embodiment shown inFIG. 1, caches40are able to exercise certain control functions over storage devices50. These control functions may alternatively be realized by hardware devices such as disk controllers (not shown), which are linked to caches40.

Each storage module36is operative to monitor its state, including the states of associated caches40, and to transmit configuration information to other components of storage subsystem20for example, configuration changes that result in blocking intervals, or limit the rate at which I/O requests for the sets of physical storage are accepted.

Routing of commands and data from HBAs28to clustered storage controller34and to each cache40may be performed over a network and/or a switch. Herein, by way of example, HBAs28may be coupled to storage modules36by at least one switch (not shown) of SAN26, which can be of any known type having a digital cross-connect function. Additionally or alternatively, HBAs28may be coupled to storage modules36.

In some embodiments, data having contiguous logical addresses can be distributed among modules36, and within the storage devices in each of the modules. Alternatively, the data can be distributed using other algorithms, e.g., byte or block interleaving. In general, this increases bandwidth, for instance, by allowing a volume in a SAN or a file in network attached storage to be read from or written to more than one given storage device50at a time. However, this technique requires coordination among the various storage devices, and in practice may require complex provisions for any failure of the storage devices, and a strategy for dealing with error checking information, e.g., a technique for storing parity information relating to distributed data. Indeed, when logical unit partitions are distributed in sufficiently small granularity, data associated with a single logical unit may span all of the storage devices50.

While such hardware is not explicitly shown for purposes of illustrative simplicity, clustered storage controller34may be adapted for implementation in conjunction with certain hardware, such as a rack mount system, a midplane, and/or a backplane. Indeed, private network46in one embodiment may be implemented using a backplane. Additional hardware such as the aforementioned switches, processors, controllers, memory devices, and the like may also be incorporated into clustered storage controller34and elsewhere within storage subsystem20, again as the skilled artisan will appreciate. Further, a variety of software components, operating systems, firmware, and the like may be integrated into one storage subsystem20.

Storage devices50may comprise a combination of high capacity hard disk drives and solid state disk drives. In some embodiments each of storage devices50may comprise a logical storage device. In storage systems implementing the Small Computer System Interface (SCSI) protocol, the logical storage devices may be referred to as logical units, or LUNs. While each LUN can be addressed as a single logical unit, the LUN may comprise a combination of high capacity hard disk drives and/or solid state disk drives.

Examples of adapters32and42include switched fabric adapters such as Fibre Channel (FC) adapters, Internet Small Computer System Interface (iSCSI) adapters, Fibre Channel over Ethernet (FCoE) adapters and Infiniband™ adapters.

FIG. 2is a block diagram of a facility60configured to process proxy input/output requests, in accordance with an embodiment of the present invention. In the description herein, storage controllers34and their respective components may be differentiated by appending a letter to the identifying numeral, so that facility60comprises host computer22and storage controllers34A and34B that are configured to communicate with each other via SAN26. In embodiments herein, storage controller34A may also be referred to as a first storage controller34or as a proxy storage controller34, and storage controller34B may also be referred to as a second storage controller34or an owner storage controller34.

Host computer22communicates with SAN26via ports62. Module36comprises a processor64and a memory66, and communicates with SAN26via ports68. In some embodiments ports62and68may comprise SCSI ports, and the SCSI ports may be configured within module36. In embodiments herein, ports68A may also be referred to as proxy ports and ports68B may also be referred to as owner ports.

While for purposes of illustrative simplicity, the configuration inFIG. 2shows module36comprising a single storage device50storing a single logical volume70, module36typically comprises multiple storage devices50storing multiple logical volumes70. Additionally, a given logical volume70may be stored across multiple storage devices50in a given storage controller34.

In embodiments of the present invention, processor64A executes, from memory66A, a proxy layer72that enables processor64A to receive, from host computer22, an I/O request for volume70B (also referred to herein as a request to perform an I/O operation on volume70B), to convey the I/O request to the owner storage controller, to receive a response for the I/O request from the owner storage controller, and to convey the response to the host computer. Processor64B executes, from memory66B, an owner layer74that enables processor64B to receive, from the proxy storage controller, an I/O request from host computer22for volume70B, to process the I/O request, and to convey a response to the I/O request to the proxy storage controller. In embodiments herein, an I/O request that storage controller34A receives from host computer22for volume70B that that is forwarded to storage controller34B may also be referred to as a proxy I/O request.

Processor64typically comprises a general-purpose central processing unit (CPU), which is programmed in software to carry out the functions described herein. The software may be downloaded to module36in electronic form, over a network, for example, or it may be provided on non-transitory tangible media, such as optical, magnetic or electronic memory media. Alternatively, some or all of the functions of processor64may be carried out by dedicated or programmable digital hardware components, or using a combination of hardware and software elements.

Proxy Storage Controller I/O Request Processing

In embodiments of the present invention, storage controller34A system can be configured as a proxy for logical volume70B that is stored on the storage controller34B. In operation, volume70B is mapped between host computer22and storage controller34A, even though volume70B is physically stored on storage controller34B.

FIG. 3is a flow diagram that schematically illustrates a method for storage controller34A to process a proxy I/O request received from host computer22, in accordance with an embodiment of the present invention. In a first receive step80, processor64A receives, from host computer22, an I/O request for volume70B, and processor64A configures the I/O request as a proxy I/O request upon determining that volume70B is stored on storage controller34B.

In a first identification step82, processor64A identifies an initial port68B on storage controller34B for processing the I/O request. In some embodiments the initial port comprises the least busy port68B. In a first convey step84, processor64A conveys a probe request to initial port68B to verify an availability of volume70B for the I/O request. For example, volume70B may currently be reserved by a different host computer22, or volume70B may have a read-only status and the I/O request may be for a write operation.

The probe request typically includes a header such as a SCSI command description block (CDB). In some embodiments, processor64A can split the I/O request into multiple sub-requests, and the probe request may include a count of the sub-requests. Splitting an I/O request into multiple sub-requests is described in more detail in U.S. Patent Application “Load Balancing Input/Output Operations Between Two Computers”, referenced above.

Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.

Additionally, since the I/O request can be divided into multiple sub-requests, the probe request also enables processors64A and/or64B to detect when the I/O operation indicated by the I/O request is complete, and the volume is consistent. For example, prior to taking a snapshot of volume70B, processor64can verify that any pending sub-requests are completed, thereby ensuring volume integrity.

In a first decision step86, if processor64A receives a response from processor64B indicating an availability of logical volume70B for the I/O request, then in second convey step88, processor64A starts conveying the proxy I/O request to initial port68B. In embodiments where processor64A splits the I/O request into multiple sub-requests, processor64A can start sending each of the sub-requests to initial port68B. In the example described in the flow diagram shown inFIG. 3, processor64A conveys a probe request prior to conveying the sub-requests. In some embodiments, processor64A can incorporate the probe request into the first sub-request conveyed to processor64B.

In a second decision step90, if processor64A does not detect a failure of initial port68B while conveying the I/O request, then in a third convey step92, processor64A completes conveying the I/O request to the initial port. For example, in embodiments where processor64A splits the I/O request into multiple sub-requests, processor64A completes conveying all the sub-requests.

In a second receive step94, processor64A receives a result of the I/O request from initial port68B. For example, if the I/O request comprises a read data request, then the response may include data read from volume70B. Likewise, if the I/O request comprises a write data request, then the response may include an acknowledgement that the data was written successfully to logical volume70B. Finally, in a fourth convey step96, processor64A conveys the result of the I/O request to the host computer, and the method ends.

Returning to step90, if processor64A detects a failure of initial port68B while conveying the I/O request, then in a third identification step98, processor64A identifies a non-conveyed portion of the I/O request. For example, in embodiments where processor64A splits the I/O request into multiple sub-requests, upon detecting a failure of initial port68B, processor64A can identify any non-conveyed sub-requests (i.e., sub-requests that are still waiting to be conveyed to processor64B).

In a third identification step100, processor64A identifies a subsequent port68B on storage controller34B. In embodiments herein, initial port68B may also be referred to as first port68B, the subsequent port68B may also be referred to as second port68B. As described supra when identifying the initial port, the subsequent port may comprise the least bust port68B.

In a fourth convey step102, processor64A conveys a continuation probe to subsequent port68B. In some embodiments, the continuation probe is similar to the probe request conveyed in step84in the sense that it initializes a context on storage controller34B for receiving sub-requests. However, the continuation probe may skip any validity checks (e.g., checking for reservations) for processing the I/O request.

In a fifth convey step104, upon receiving an response from processor64B indicating that the continuation probe was received, processor64A conveys the non-completed portion (e.g., the identified non-conveyed sub-requests) of the I/O request to subsequent port68B, receives, in a third receive step106, the result of the I/O request from the subsequent port, and the method continues with step96. The response to the continuation probe verifies successful connectivity to storage controller34A, thereby setting up a context for an atomic I/O operation comprising the non-completed portion of the I/O request.

Upon a failure of the initial port, there may still be I/O requests (or responses to I/O requests) pending on the initial port. In some embodiments the continuation probe can “clean-up” any pending sub-requests still pending on the initial port. In an alternative embodiment, processor64A can convey a separate message to processor64B to perform a clean-up on the initial port.

Returning to step86, if processor64A receives a response from processor64B indicating that logical volume70B is not available for the I/O operation, then processor64A conveys a message indicating the non-availability of volume70B to the host computer, and the method ends.

Owner Storage Controller I/O Request Processing

FIG. 4is a flow diagram that schematically illustrates a method for storage controller34B to process a proxy I/O request received from storage controller34A, in accordance with an embodiment of the present invention. In first receive step110, processor64B receives, via an initial port68B, a probe request to verify an availability (as described supra) of logical volume70B for processing an I/O request from host computer22.

In a first decision step112, if logical volume70B is available for the I/O request, then in a first convey step114, processor64B conveys, via initial port68B, a message confirming the volume availability for the I/O request. In a second receive step116, processor64B starts receiving, via initial port68B the proxy I/O request from processor64A. In embodiments where processor64A splits the proxy I/O request into multiple sub-requests, receiving the proxy I/O request comprises receiving the multiple sub-requests, and using information included in the probe request to “re-assemble” the sub-parts into the proxy I/O request.

In a second comparison step118, if the proxy I/O request comprises multiple sub-requests, and processor64B receives a continuation probe on a subsequent port68B (different than initial port68B) prior to receiving all the sub-requests, then in a third receive step120, processor64B completes receiving the proxy I/O request via subsequent port68B. In a first processing step122, processor64B processes the proxy I/O request via subsequent port68B, and the method ends.

For example, if the proxy I/O request comprises a request to read data from logical volume70B, then processor68B can retrieve the data from the logical volume, and convey the retrieved data to processor64B via subsequent port68B.

While the example shown inFIG. 4describes a single failure of an owner port while processing a set of sub-requests (i.e., for a single I/O requests), a failure of two or more ports is considered to be within the spirit and scope of the present invention. For example, processor64A may detect a failure of the subsequent port, and an additional continuation probe can be conveyed to a further (i.e., a third) owner port64B to complete processing the I/O request using embodiments described herein.

Returning to step118, if processor64B does not receive a continuation probe while receiving the proxy I/O request, then in a fourth receive step124, processor64B completes receiving the proxy I/O request via initial port68B. In a second processing step126, processor64B processes the proxy I/O request via the initial port in and the method ends.

Returning to step112, if logical volume70B is not available for the proxy I/O request, then in a second convey step128, processor64B conveys a non-availability message to processor64A (i.e., in response to the probe request), and the message ends.