CACHE LOAD BALANCING IN STORAGE CONTROLLERS

• US 20140229658A1
• Filed: 02/14/2013
• Published: 08/14/2014
• Est. Priority Date: 02/14/2013
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: LSI Corporation (Broadcom, Inc.)
• Inventors: Maharana, Parag R., Sampathkumar, Kishore K.
• Granted Patent: US 9,110,813 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/0802 Addressing of a memory level in which the access to the desired data or data block requires associative addressing means, e.g. caches
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 13/28 using burst mode transfer, e.g. direct memory access DMA, cycle steal G06F13/32 takes precedence
• CPC Class Codes: G06F 13/4221 being an input/output bus, e.g. ISA bus, EISA bus, PCI bus, SCSI bus
• CPC Class Codes: G06F 2212/1036 Life time enhancement
• CPC Class Codes: G06F 2212/222 Non-volatile memory
• CPC Class Codes: G06F 2212/262 configured as RAID
• CPC Class Codes: G06F 2212/283 Plural cache memories
• CPC Class Codes: G06F 2212/604 Details relating to cache allocation

Abstract

Methods and structure are provided for cache load balancing in storage controllers that utilize Solid State Drive (SSD) caches. One embodiment is a storage controller of a storage system. The storage controller includes a host interface operable to receive Input and Output (I/O) operations from a host computer. The storage controller also includes a cache memory that includes an SSD. Further, the storage controller includes a cache manager that is distinct from the cache memory. The cache manager is able to determine physical locations in the multiple SSDs that are unused, to identify an unused location that was written to a longer period of time ago than other unused locations, and to store a received I/O operation in the identified physical location. Further, the cache manager is able to trigger transmission of the stored I/O operations to storage devices of the storage system for processing.

Claims

1. A storage controller of a storage system, the storage controller comprising:

a host interface operable to receive Input and Output (I/O) operations from a host computer;

a cache memory comprising a Solid State Drive (SSD); and

a cache manager that is distinct from the cache memory and that is operable to determine physical locations in the multiple SSDs that are unused, to identify an unused location that was written to a longer period of time ago than other unused locations, and to store a received I/O operation in the identified physical location,

the cache manager further operable to trigger transmission of the stored I/O operations to storage devices of the storage system for processing.

2. The storage controller of claim 1, wherein:

the cache manager is further operable to determine that a set of cached I/0 operations are directed to different storage devices along signaling pathways that share at least one common device, and to alter one of the set of cached I/O operations to direct it along a new signaling pathway that does not share a common device.

3. The storage controller of claim 1, wherein:

the cache manager is further operable to access an index to determine the identified physical location, and to alter the index after the received I/O operation is stored so that the index identifies a new unused physical location.

4. The storage controller of claim 1, wherein:

the storage devices implement a striped Redundant Array of Independent Disks (RAID) volume, and

the cache manager is further operable to write each received I/O operation to the cache as one or more full stripes of RAID data.

5. The storage controller of claim 4, wherein:

the cache memory comprises multiple SSDs, and

the cache manager is further operable to write each block of the stripe to a different SSD.

6. The storage controller of claim 1, wherein:

the cache comprises a Single-Level Cell (SLC) SSD and a Multi-Level Cell (MLC) SSD, and

the cache manager is further operable to review the received I/O operation to determine whether the I/O operation is a write operation, to store the I/O operation in the MLC SSD if the I/O operation is not a write operation, and to store the I/O operation in the SLC SSD if the I/O operation is a write operation in order to increase the operational lifetime of the MLC SSD.

7. The storage controller of claim 1, wherein:

the cache comprises multiple SSDs, and

the cache manager is further operable to determine, while operating, that the number of SSDs implementing the cache has changed, and to update the determined set of physical locations to reflect the change.

8. A method for operating a storage controller of a storage system, the method comprising:

receiving Input and Output (I/O) operations from a host computer at a storage controller that includes a cache memory that comprises a Solid State Drive (SSD);

determining physical locations that are unused in the cache memory, via a cache manager of the storage controller that is distinct from the cache memory;

identifying an unused location that was written to a longer period of time ago than other unused locations;

storing a received I/O operation in the identified physical location; and

transmitting the stored I/O operation from the storage controller to a storage device of the storage system.

9. The method of claim 8, further comprising:

determining that a set of cached I/O operations are directed to different storage devices along signaling pathways that share at least one common device; and

altering one of the set of cached I/O operations to direct it along a new signaling pathway that does not share a common device.

10. The method of claim 8, further comprising:

accessing an index to determine the identified physical location; and

altering the index after the received I/O operation is stored so that the index identifies a new unused physical location.

11. The method of claim 8, wherein:

the storage devices implement a striped Redundant Array of Independent Disks (RAID) volume, and the method further comprises;

writing each received I/O operation to the cache as one or more full stripes of RAID data.

12. The method of claim 11, wherein:

the cache memory comprises multiple SSDs, and the method further comprises;

writing each block of the stripe to a different SSD.

13. The method of claim 8, wherein:

the cache comprises a Single-Level Cell (SLC) SSD and a Multi-Level Cell (MLC) SSD, and the method further comprises;

reviewing the received I/O operation to determine whether the I/O operation is a write operation;

storing the I/O operation in the MLC SSD if the I/O operation is not a write operation; and

storing the I/O operation in the SLC SSD if the I/O operation is a write operation in order to increase the operational lifetime of the MLC SSD.

14. The method of claim 8, wherein:

the cache comprises multiple SSDs, and the method further comprises;

determining, while actively operating the storage controller, that the number of SSDs implementing the cache has changed; and

updating the determined set of physical locations to reflect the change.

15. A non-transitory computer readable medium embodying programmed instructions which, when executed by a processor, are operable for performing a method comprising:

receiving Input and Output (I/O) operations from a host computer at a storage controller that includes a cache memory that comprises a Solid State Drive (SSD);

determining physical locations that are unused in the cache memory, via a cache manager of the storage controller that is distinct from the cache memory;

identifying an unused location that was written to a longer period of time ago than other unused locations;

storing a received I/O operation in the identified physical location; and

transmitting the stored I/O operation from the storage controller to a storage device of the storage system.

16. The medium of claim 15, the method further comprising:

determining that a set of cached I/O operations are directed to different storage devices along signaling pathways that share at least one common device; and

altering one of the set of cached I/O operations to direct it along a new signaling pathway that does not share a common device.

17. The medium of claim 15, the method further comprising:

accessing an index to determine the identified physical location; and

altering the index after the received I/O operation is stored so that the index identifies a new unused physical location.

18. The medium of claim 15, wherein:

the storage devices implement a striped Redundant Array of Independent Disks (RAID) volume, and the method further comprises;

writing each received I/O operation to the cache as one or more full stripes of RAID data.

19. The medium of claim 18, wherein:

the cache memory comprises multiple SSDs, and the method further comprises;

writing each block of the stripe to a different SSD.

20. The medium of claim 15, wherein:

the cache comprises a Single-Level Cell (SLC) SSD and a Multi-Level Cell (MLC) SSD, and the method further comprises;

reviewing the received I/O operation to determine whether the I/O operation is a write operation;

storing the I/O operation in the MLC SSD if the I/O operation is not a write operation; and

storing the I/O operation in the SLC SSD if the I/O operation is a write operation in order to increase the operational lifetime of the MLC SSD.