# Patent

## Title
Tape failover across a cluster

## Abstract

A security appliance that encrypts and decrypts information is installed in each of redundant multi-paths between a host system and a back up tape storage system. The host system is arranged to detect failures in a primary path to the tape system being used. When the failure is detected, the host system enables transfers to the same tape system through an alternative path. Encryption keys and host/tape designators (identifiers) are broadcast among the security appliances in the alternative data paths. When the host system switches from the primary path to the secondary path, even though the secondary security appliance did not generate the encryption keys, the secondary path security appliance will have such keys and will properly encrypt and transfer data from the host to the tape system. The secondary will also properly retrieve encrypted data from the tape system, decrypt it and deliver it to the host. All of these operations will be transparent (invisible) to a running application in the host.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of commonly assigned U.S. patent application Ser. No. 11/606,508, which was filed on Nov. 30, 2006 now U.S. Pat. No. 7,853,019, by Anant Chaudhary et al., for a TAPE FAILOVER ACROSS A CLUSTER and is hereby incorporated by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to networked magnetic storage tape systems, and more particularly to tape systems connected via a tape driver system that provide tape failover capability. Tape failover refers to having alternative paths between a host and a tape system, where when one path fails the other path is seamlessly enabled and the first path disabled.
2. Background Information
One tape failover system was developed by IBM for backing up system memories of host computer systems and is referred to as Atape driver running under the AIX operating system. Atape driver refers to IBM AIX Enhanced Tape and Medium Changer Device Driver. AIX is a proprietary operating system developed by IBM based on a UNIX system. AIX comes from Advanced IBM Unix or, more recently, from Advanced Interactive eXective. For more discussion on the Atape driver and AIX, see IBM publication, entitled, IBM Magstar Tape Drives—AIX High Availability SAN Failover for 3590, by Rob Bashand and Jim Ayres, and published Jun. 12, 2001 by IBM Corp., Tucson, Ariz., U.S.A. This publication is incorporated herein by reference.
The AIX Atape driver provides up to fifteen alternative parallel paths to a single tape drive system. When a failover occurs, the Atape driver will enable one of the alternative paths invisibly to applications running on the host computer system.
Operations of tape back up systems are well known in the art, and are only briefly described herein. Generally, the first block, block 0, is written by the host onto a blank tape. Block 0 will contain label and header-type information, e.g. index of files within the image, etc., so that the tape and its contents can be identified by the host. Block 0 is written and data blocks or files are then sequentially written onto the tape. The tape may be physically unloaded from the tape drive and stored. When the host system memory needs to be restored, the tape is reloaded onto the tape drive, the host reads block 0 and replaces the host's memory contents with the data from the tape. Protocols, file structures, error detection and correction that are used for these operations are well known in the art. If there is a failover, the Atape driver enables an alternative path to the tape system, and operations continue as if there were no failure.
Consider a tape failover environment, wherein a security appliance or system is located “in-line” in each of the separate paths running from a host system to a single tape system. The security appliance is configured to encrypt data generated by the host system for secure storage on the tape system. In such an environment, block 0 will contain encryption information. The security appliance encrypts data coming from the host and delivers it to the tape and decrypts data coming from the tape system (when the tape is restoring the host memory) and delivers it to the host. The Host/Atape driver and tape systems operate as though the security appliance was not there.
Limitations, however, occur since one security appliance may NOT have the encryption key for a tape written through another security appliance. If a failover occurs, the Atape driver diverts the data flow to an alternative path. The operation will fail, however, since the encryption key is not known to the security appliance in the alternative path.
The present invention is concerned, inter alia, with the above limitations.
Encryption systems and keys are well known in the art, including public/private key operations, and these systems and processes are generically described as they apply to specific operations in examples of the present invention. The use herein of “encryption key” refers to all the encryption information needed to encrypt and decrypt data.
SUMMARY OF THE INVENTION
The limitations of the prior art are addressed by providing a system for tape failover across a cluster of security appliances coupled between a host system and a tape back up system. According to the invention, when the data on a tape is encrypted, the encryption key may be broadcast to all security appliances in the cluster. This allows the other encryption devices, that provide alternative paths (APs) between a host system and a tape back up, to successfully encrypt and store the data onto the tape, and later decrypt the tape data retrieved from the tape. In a clustered system with alternative paths, one primary path and the other secondary paths, between a host system and a tape back up system, where all paths have in-line security appliances that encrypt and decrypt data, the security appliances must share the encryption data. When the host system writes to block 0 on the tape, the primary security appliance will have an encryption key and broadcast that key to other security appliances clustered with the primary. The secondary security appliances will have the encryption key and be able to encrypt and decrypt data traveling from host to tape and visa versa, if needed. The host, tape and security appliances may be assigned LUN's (Logical Unit Numbers) and WWN's (World Wide Numbers) or other equivalent designators or identifiers so that the devices will able to determine which security appliances in the primary path and which are in the alternative or secondary paths.
In other examples the encryption keys may be stored in an external key server.
It will be appreciated by those skilled in the art that although the following Detailed Description will proceed with reference being made to illustrative embodiments, the drawings, and methods of use, the present invention is not intended to be limited to these embodiments and methods of use. Rather, the present invention is of broad scope and is intended to be defined as only set forth in the accompanying claims.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention description below refers to the accompanying drawings, of which:
FIG. 1 is a block diagram/schematic illustrating a typical cluster of security appliances with one security appliance in each path from a host and a tape system;
FIG. 2 is a block diagram of a security appliance; and
FIGS. 3, 4, 5 and 6 are flow chart examples illustrating the invention's operations.



DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
FIG. 1 shows a host computer system running the AIX operating system (AIX host 2) and an Atape driver 4. HBA's 6, 8 (Host Bus Adapters) connect to two security appliances 10, 12, respectively, that are interconnected as a cluster providing alternative separate paths to a single tape system 18. The security appliances connect to the host HBA's 6 and 8 through separate HBA's 14 and 16, respectively. The two security appliances continue the two paths and connect to HBA ports 15 and 17, respectively, on the single tape system 18. The ports on the security appliances may mimic the sending and receiving HBA's on the host and the tape system, respectively.
In this example, the tape system complies with the known FCP-2 (Fibre Channel Protocol-2) that contains an error recovery mechanism for FCP-2. At the protocol layer, re-tries are performed and recovery made, if possible. However, all such re-tries are via the same path from the host to the tape system, and, so, if a failover occurs along the path, the error recovery will also fail. Atape driver 4 addresses this type of failure by enabling an alternative path to the tape system. When a permanent error occurs on the primary path, the Atape driver automatically initiates error recovery and continues the operation on an alternative path (AP) without interrupting the application running on the host that initiated the back up operation. The Atape driver keeps track of the state of the tape system, any SCSI (Small Computer System Interface, which is often used with disk and tape systems) reservation, and current tape position. When a failover occurs the Atape driver will restore the previous system state, any SCSI reservation, and tape position prior to re-trying the failed operation.
As mentioned above, an Atape driver supports many alternative paths, but only two such paths are discussed in this example. Consider that the AIX/Atape driver host system selects the primary path via security appliance 10 and an alternative secondary path via security appliance 12. If during a back up operation, the primary path fails, the Atape driver detects the failure, e.g. by not receiving an acknowledgement from the tape system, and switches to the secondary path. However, the switch over will fail, as discussed herein, unless the security appliance in the secondary path has the necessary encryption key.
As discussed below, the encryption keys are, for example, generated by the security appliance when block 0 is written onto a tape. The SEP (Storage Encryption Processor—that could be any generic processor so arranged) 270 processor may generate the encryption key or an LKM (Lifetime Key Management Server which stands for any key server so arranged) 28, FIG. 1, may be used as a source of encryption keys.
The security appliance 10 comprises one or more network adapters 220 with HBA ports that physically connect to the Atape driver HBA 6 and to the tape system 18 HBA port 15, respectively.
Similarly, the security appliance 12 has a network adapter 220′ with HBA's that physically couple the Atape driver HBA 8 to the tape system 18, HBA port 17, respectively.
The network adapters 220 and 220′ also contains, in this example, HBA's configured as Ethernet ports 24 and 26 that are correspondingly connected to an Ethernet cable 19. The security appliances 10, 12, . . . n, are all coupled together as a cluster that shares information via the Ethernet cable 19. However, as would be known to one skilled in the art, the coupling of the clustered security appliances among each other may be accomplished via point-to-point links in a daisy chain, star or tree configuration, or via wide area networks, virtual private networks implemented over a public network (Internet) or shared local area networks.
In this example, the connections from unit 10 to the Ethernet may be made via interface cards, HBA 24 and ET1, that have the mechanical, electrical and signaling circuitry needed to connect the security appliance 10 to the Ethernet cable 19. In this example, the file structure and control messaging used by the clustered security appliances over the Ethernet is the IP protocol. But as known to those skilled in the art many other hardware and software systems may be used for inter-communicating among security appliances.
In one example, the hardware/software arrangement used to connect the host system 2 to a tape system 18 is FC (Fibre Channel), but other commonly used configurations for networked storage networks, in this case back up tape systems, may be used. Some such arrangements include SCSI protocols, including SCSI encapsulated over TCP (iSCSI—Internet SCSI) and SCSI encapsulated over FC (FCP—Fibre Channel Protocol), wherein the network adapters 220 and 220′ may comprise host bus adapters (HBAs) having the mechanical, electrical and signaling circuitry needed to connect the appliances to, for example, a FC network.
FIG. 2 is a schematic block diagram of the multi-protocol security appliance 10 or 12 that may be advantageously used with the present invention. As used herein, a security appliance denotes a computer system having features such as security service management for users (system administrators) and clients for attached storage devices. The security appliance typically comprises at least one processor, e.g., central processing units (CPU 220), a memory 210, at least one network adapter 220 (or 220′) and at least one storage encryption processor (SEP 390) interconnected by a system bus 240. The bus 240 may be a conventional Peripheral Component Interconnect (PCI) bus, or an address, data, control bus found for virtually any CPU. The SEP 270 is configured to perform all encryption and decryption operations for the security appliance and to protect the encryption information from retrieval via an external entity.
The memory 210 illustratively comprises storage locations that are addressable by the processors and adapters for storing software programs and data structures associated with the present invention. The processor and bus adapters may, in turn, comprise processing elements and/or logic circuitry configured to execute the software programs and manipulate the data structures. An operating system 212, portions of which are typically resident in memory and executed by the processing elements, functionally organizes the appliance 10 or 12 by, inter alia, invoking security operations in support of software processes run by the appliance.
The problem, mentioned above, is that the security appliance 12, when enabled as a secondary path, may not have the encryption key (in its cache or anywhere else) for a tape written through security appliance 10. This will happen if any of the clustered security appliances do not have the same encryption key. The security appliance 10 receives information for a tape when the tape is labeled, i.e. when block 0 is physically written on the tape. The security device 10 generates the encryption key at that time (or retrieves it from the LKM) and uses that key to encrypt data from the host and write that encrypted data onto the tape. The security appliance 10 also uses the encryption information to decrypt information coming from the tape to be restored to the host. However, if the tape was previously written to, and the Atape driver enabled a secondary path to the tape via security appliance 12, that different security appliance 12 has the encryption key (and device identification information) developed by the primary security appliance in order to function.
FIG. 3 is a representative flow chart of steps illustrating the security appliance 10 operating as the primary path from the host to the tape system. The security appliance, as mentioned above, encrypts data to be stored on the tape and decrypts the data when restoring the data to the host.
In step 300, the host issues a write block 0 command to the tape via Atape driver 4 and security appliance 10. This may happen, for example, when a new tape is loaded onto the tape drive or when the system administrator so determines. The security appliance receives the write block 0 and generates an encryption key in step 302. With the tape failover driver operation enabled (the Atape Enabled in one embodiment) in step 304, the security appliance may broadcast at least the encryption information to all the security appliances clustered with security appliance 10 via the Ethernet cable 19. In step 308, the security appliance 10 then writes block 0 (in clear—not encrypted, although in other examples block 0 may be encrypted). Data sent by the host to the tape system is encrypted with the encryption key in step 310 and written onto the tape by the primary security appliance 10. If the primary path fails, the Atape driver 4 will detect the failure and switch from the primary path to the secondary path via security appliance 12.
As long as the tape remains on the tape drive 311 (NO), 312, the data from the host may be encrypted and stored on the tape. When the tape is unloaded 313 (YES), or taken off the physical tape drive system, and the Atape drive is enabled in step 314, the security appliance 10 in step 316 broadcasts the encryption information to those security appliances clustered with security appliance 10. If there is no tape on the tape drive, the encryption key held in security appliance 10 may be allowed to expire. The process then returns as in step 300. When a new tape is loaded, the operation repeats. In one example, the security appliances may routinely broadcast, e.g. on a timed “heartbeat,” to each other, via the Ethernet, to keep the others informed of those tape systems in the cluster.
Steps 304 and 314, (tape failover drive Enabled), illustrate a feature of this embodiment. Each security appliance (10, 12, etc.) can be configured to not respond to the Atape driver operation, that is, the security appliances do not broadcast the encryption information to clustered security appliances, and, so, if the Atape driver enables another path with a security appliance, the backup operation will fail due to lack of encryption information as explained above.
FIG. 4 illustrates a process executed at security appliance 12 when enabled as an alternative path by Atape driver. In this case, security appliance 10 had already broadcast its encryption information to security appliance 12. If, for some reason, a broadcast containing the tape encryption key, step 402, from security appliance 10 was not received, any data received from the host via security appliance 12 is rejected in step 404. However, if the tape encryption key has been received from security appliance 10, the security appliance in step 406 forces the host to discover the current tape position. Once the host issues a command to discovery position, the process continues at step 408, where the security appliance by accepts data from the host system and encrypts and stores it on the tape. When the host requires the contents of the tape to be restored from the tape, the security appliance 12 receives such a command and retrieves the data from the tape, decrypts it and returns it to the host system. When the tape is unloaded, the process continues as at point B in FIG. 3. The security appliance 12 broadcasts the encryption operation to the cluster and expires the encryption key. The security appliance then waits for a host system write to block 0. In one example, security appliance 12 may initially be in the primary path, but, after a failover that is resolved, security appliance 10 may 1 be in the primary path.
FIGS. 5 and 6 are representative flow charts for the case of data being read from a tape. The flow is very similar to the case of a write and many parallels exist. When the host loads a new tape, it first reads block 0. When this block is read, the security appliance retrieves encryption key information from the block 500. This information is broadcast 502 to all other cluster members. As long as the tape remains in the drive, data on the tape continues to be decrypted 504. If the tape is ejected 506, the key is expired 508 and this expiration is broadcast 510 to the other cluster members. On a failover event 600, the new path forces the host to discover the current tape position 602. Once the position is known 604, the process continues with the host reading data and the security appliance decrypting it 606.
When the system described in the FIGS. 1-6 is initialized, the security appliances are clustered and are configured via the Ethernet cable 19, as shown, to share information, including encryption keys and system information that the administer might determine. In the configuration of FIG. 1, the system may be initialized by an administrator manually entering identifiers of which tape system and which host is connected to each security appliance in a cluster. The information may be entered as a data structure illustratively embodied as a table within the security appliance. Later, the host system writes to block 0 and the security appliance in the primary path broadcasts the encryption information keys it uses for encryption/decryption along with its stored designators for its host and tape systems. All the clustered security appliances receive that information, and those clustered appliances connected to the same host and tape system may be the alternative path enabled by the Atape drive system. When a failover occurs in the primary path, the Atape driver will enable an alternative path, but the tape position may be lost. Even though the Atape driver retains the tape position, the primary security appliance may have acknowledged successful data block that was, in fact, not successfully stored. That is, the security appliance may have issued an early ACK (acknowledge). In this example, the secondary security appliance sends to the Atape driver a SCSI “check condition” command, with a sense code indicating that the tape position is lost. Note that the security appliance is connected to both the host and the tape system via FC. In this context, the FC is adapted to operate in a block access protocol. In this case, an SCSI protocol encapsulation—FC, e.g., FCP. SCSI is a peripheral I/O (Input/Output) interface with a standard, device independent protocol allowing many types of peripheral devices (disks, tapes,) to attach to the host, or client. The Atape driver, in response, searches for and finds the correct tape position. If that position is the end of the last successful data block transferred, and when the tape is so positioned, the Atape driver sends the last (failed) data block (as described above for the Atape driver). The security appliance in the alternative path will have all the encryption information needed to continue the back up operation seamlessly. The host, Atape driver, security appliance and tape system may be arranged so that only the security devices on alternative paths to the tape system are clustered on one Ethernet cable. In such a case, any primary path giving up operation to a secondary path broadcasts the encryption information to the security appliances on the Ethernet, since the host and tape systems are already known (from initialization) to each security appliance.
Here, the security appliances are connected by FC links on both their host and storage sides. Any new FC device discovered by the security appliance on one side, say the host side, is reported to the device on the other, the tape system, side. The FC devices are identified by both a WWN (World Wide Number) and an LUN (Logic Unit Number) that have been assigned by an administrator. The clustered security appliances, as discussed above, communicate over the Ethernet, in this example, using the IP protocol.
Typically, the host is the initiator and the storage device is the target that responds to the host's commands. Both the host and the tape system have end point addresses that, as in FC protocol, include WWN as an eight byte number and an LUN.
In other embodiments, the security appliance may scan and detect connected tape systems by having a library of WWNs and LUNs designating tape systems. The security appliance may then be scanned by a host, where the security appliance returns the tape WWN and LUN. The host scans and finds the tape system transparently with respect to the security appliance. However, the security appliance may, if set up initially by an administrator, return its own WWN and LUN identifier to the host and, in effect, disable the Atape driver operation. In this arrangement, the host can still access the tape system, even if the tape system was not initialized (block 0) by the security appliance. However, in this instance the alternative paths operation by the Atape driver may be thwarted.
When implementing the present invention, the receipt of data by the security appliance, and its acknowledgment of that receipt, may cause a limitation if a failure occurs between the security appliance and the tape system. In such a case, the host will have incorrect information about the number of blocks successfully written to the tape. When the switch to the alternate path occurs, the host, via Atape driver, will position the tape farther along the tape than the actual number of successfully written blocks on the tape. If this occurs, the AIX operating system will read a blank and the system should fail. However, the system may, via the alternative path, always rewind one block, read that block if present and then continue.
The above discussion includes use of the AIX operating system and the Atape driver. However, the present invention may be advantageously used with virtually any tape failover system running under virtually any operating system. The present invention is not specific to one tape driver and/or one operating system.
It will be apparent to those skilled in the art that other processing and memory means, including various computer readable media, may be used for storing and executing program instructions pertaining to the invention described herein.

## Claims

1. A method comprising:
establishing a primary path and a secondary path from a host to a backup system, wherein a first security appliance, comprising a processor, is logically interconnected on the primary path between the host and the backup system and a second security appliance is logically interconnected on the secondary path between the host and the backup system;
intercepting, by the first security appliance, data sent on the primary path between the host and the backup system, wherein the first security appliance utilizes an encryption key to perform at least one of encrypting the data and decrypting the data sent on the primary path; and
broadcasting, by the first security appliance, the encryption key to the second security appliance over a communication channel between the first security appliance and the second security appliance in response to generating the encryption key.

2. The method of claim 1 wherein broadcasting the encryption key to the second security appliance further comprises routinely broadcasting the encryption key to the second security appliance.

3. The method of claim 1 further comprising:
labeling the host and the backup system with logical designators, and broadcasting the logical designators to the second security appliance.

4. The method of claim 3 wherein the logical designators include a World Wide Number and a logical Unit Number.

5. The method of claim 1 further comprising generating the encryption key when the backup system is initialized.

6. The method of claim 1 wherein the first security appliance generates the encryption key.

7. The method of claim 1 further comprising:
generating the encryption key at a storage encryption server; and
retrieving the encryption key from the storage encryption server by the first security appliance.

8. The method of claim 1 further comprising:
detecting an error in the sent data along the primary path;
in response to the detecting, disabling the first security appliance logically interconnected on the primary path; and
enabling the second security appliance in the secondary path to encrypt and decrypt data between the host and the backup system.

9. The method of claim 1 wherein the backup system is a tape backup system.

10. A system comprising:
at least two security appliances each comprising a processor and a memory, with a first security appliance logically interconnected on a primary path and a second security appliance logically interconnected on a secondary path between a host and a backup system, wherein the first and second security appliances use an encryption key to perform at least one of encrypting data and decrypting data on the primary path and the secondary path;
a communication channel between the first and second security appliances; and
wherein when the backup system is initialized, the encryption key is generated in the first security appliance logically interconnected on the primary path, and the generated encryption key is broadcast to the second security appliance via the communication channel.

11. The system of claim 10 further comprising routinely broadcasting the encryption key to the second security appliance.

12. The system of claim 10 further comprising:
additional security appliances connected to the communications channel, and arranged between other hosts and other backup systems;
storage in the first and second security appliances and the additional security appliances, wherein the storage contains logic designators of each of the hosts and the backup systems; and
wherein when the backup system is initialized, the first security appliance broadcasts the encryption information and the designators of the host and backup system associated with the primary path.

13. The system of claim 12 wherein the logical designators include a World Wide Number and a Logical Unit Number.

14. The system of claim 10 wherein the first security appliance generates the encryption key.

15. The system of claim 10 further comprising a source of encryption keys, wherein when the backup system is initialized, the first security appliance retrieves encryption keys from the source.

16. The system of claim 10 wherein the first security appliance stores encryption information onto the backup system when the backup system is initialized.

17. The system of claim 10 wherein the host system determines that an error has occurred along the primary path, wherein the host system disables the first security appliance logically interconnected on the primary path and enables the second security appliance logically interconnected on the secondary path.

18. The system of claim 10 wherein the backup system is a tape backup system.

19. A non-transitory computer readable medium containing executable program instructions executable by a processor, comprising:
program instructions that establish a primary path and a secondary path from a host to a backup system, wherein a first security appliance is logically interconnected on the primary path between the host and the backup system and a second security appliance is logically interconnected on the secondary path between the host and the backup system;
program instructions that intercept data sent on the primary path between the host and the backup system, wherein the first security appliance utilizes an encryption key to perform at least one of encrypting the data and decrypting the data sent on the primary path; and
program instructions that broadcast the encryption key from the first security appliance to the second security appliance over a communication channel between the first security appliance and the second security appliance in response to generating the encryption key.

20. The non-transitory computer readable medium of claim 19 further comprising:
program instructions that detect an error in the sent data along the primary path;
program instructions that disable the first security appliance logically interconnected on the primary path; and
program instructions that enable the second security appliance in the secondary path to encrypt and decrypt data between the host and the backup system.