Electrical computers and digital processing systems: memory – Storage accessing and control – Shared memory area
Reexamination Certificate
2000-12-11
2004-01-06
Peikari, B. James (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Shared memory area
C711S150000, C711S148000, C710S240000, C710S244000, C710S045000, C710S117000, C710S124000
Reexamination Certificate
active
06675268
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to data storage in a computerized storage area network (SAN) or system utilizing redundant disk array controllers (RDAC's). More particularly, the present invention relates to a new and improved technique of managing transfers of access control of logical data volumes between the RDAC's. When a host device sends a data access request to one of the RDAC's for access to a logical data volume that is controlled by another one of the RDAC's, it is determined whether the logical data volume is currently exclusively controlled by another RDAC and the SAN is analyzed to determine whether to transfer access control of the logical data volume to the RDAC that received the data access request.
BACKGROUND OF THE INVENTION
A storage area network (SAN) typically includes a plurality of host devices connected through a switched fabric to a plurality of storage arrays. The host devices access a plurality of logical data volumes present on the plurality of storage arrays, usually on behalf of a plurality of client devices, which are typically connected to each host device. Each storage array is connected to one or more host devices through the switched fabric.
Each storage array includes multiple individual storage devices, typically arranged in a RAID (Redundant Array of Independent Drives) configuration. The RAID storage devices supply data storage space for the logical data volumes. The logical data volumes are commonly striped across multiple storage arrays, so host devices that access a given logical data volume must have a connection to each of the storage arrays that contains a portion of the logical data volume. The individual storage devices include hard drives, compact disk (CD) drives, tape drives and the like.
Each storage array also commonly includes more than one array controller, through which the storage devices and logical data volumes are accessed. Each array controller connects to the switched fabric. Thus, a data transfer path between one of the host devices and one of the storage arrays is established from the one host device, through the switched fabric, to the one array controller.
Some of the host devices may access the same storage array through more than one data transfer path through the switched fabric. Also, more than one host device may access the same logical data volume through different data transfer paths on behalf of the same or different client devices. Therefore, more than one array controller of a storage array may receive a data access request to the same logical data volume, or portion thereof, present on the storage array.
When one of the array controllers of a given storage array processes a data access request to a given logical data volume, that array controller is said to have access control or “ownership” of the logical data volume. When one array controller has ownership of the logical data volume, no other array controller in the storage array can access the logical data volume.
When an array controller receives a data access request to a logical data volume that the array controller does not currently own, it transfers ownership of the logical data volume to itself in an automatic volume transfer (AVT) process and then processes the data access request. When two or more host devices need to access the same logical data volume, but do so through different array controllers, then the array controllers repetitively transfer ownership of the logical data volume back and forth between themselves. The repetitive ownership transferring is called “thrashing.” Thrashing can severely degrade the performance of data accesses to the affected logical data volume, since significant time is taken up performing the AVT processes, instead of accessing the affected logical data volume.
When two or more host devices can access the same logical data volume through the same common array controller, then thrashing and unnecessary AVT processes are avoided, because the common array controller can process all of the data access requests. However, sometimes more than one host device cannot establish data transfer paths to the same array controller, because one host device may never have had a physical connection to the array controller or one existing physical path may have become inoperative. Therefore, transferring ownership of the logical data volume may cause one of the host devices to completely lose access to the logical data volume, yet not transferring ownership may deny access for another host device.
It is with respect to these and other background considerations that the present invention has evolved.
SUMMARY OF THE INVENTION
The present invention prevents excessive thrashing between array controllers in a storage area network (SAN) when more than one host device is attempting to access the same logical data volume through different array controllers. Thrashing is prevented by granting ownership of a logical data volume to a particular array controller for a period of exclusivity. During the exclusivity period, ownership of the logical data volume may not be transferred to another array controller. The logical data volume is said to be “sticky” to the particular array controller for the exclusivity, or “sticky,” time period, e.g. about five to ten seconds or longer depending on the situation.
The present invention also considers whether a host device may lose access to a needed logical data volume that it is currently accessing before permitting transfer of ownership of the logical data volume from the current-owner array controller to a nonowner array controller that has received a data access request to the logical data volume. Therefore, before transferring ownership of the logical data volume, the nonowner array controller examines a portion of the current topology of the SAN to determine whether any host device that requires access to the logical data volume would lose access to the logical data volume if ownership were to be transferred. The topology is the set of all connections between the host devices and the storage arrays. In this case, the nonowner array controller determines those available connections to the storage array of which it is a part, including connections through other array controllers in the same storage array. If, according to the available connections, any host device would lose access to the logical data volume upon transferring ownership from the current-owner array controller to the nonowner array controller, then preference is given to not transferring ownership. Ownership transfer is granted only if the requesting host device cannot establish a data transfer path to the current-owner array controller and the requesting host device has priority for accessing the logical data volume over the host device that is currently accessing the logical data volume.
These and other improvements are achieved by accessing a logical data volume in a storage area network that has a plurality of host devices and a storage array. The logical data volume is located on the storage array. The storage array has a plurality of array controllers through which the host devices access the logical data volume. A first array controller receives a request to access the logical data volume. The logical data volume, however, is currently owned by a second array controller, so the access request requires transfer of the ownership of the logical data volume from the second array controller to the first array controller. It is determined whether the ownership of the logical data volume by the second array controller is within an exclusive period of time. If so, then the ownership transfer is denied. However, if the ownership by the second array controller is no longer exclusive, then the ownership transfer is granted.
It is preferable that, upon granting the ownership transfer, another exclusive period of time begins. Thus, the same method may be used by the second array controller when it receives a subsequent request to access the logical data volume. It is also preferable upon granting the
Binford Charles D.
DeKoning Rodney A.
Gallagher Michael J.
Jantz Ray M.
LSI Logic Corporation
Peikari B. James
Suiter - West PC LLO
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