• Managing the FAST Cache (supported physical deployments only)

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    Managing the FAST Cache (supported physical deployments only)

    About the FAST Cache

    The FAST Cache is a large capacity secondary cache that uses SAS Flash drives to improve system performance by extending the storage system's existing caching capacity. You can configure individual pools to use the FAST Cache. When you do this, all storage resources created in those pools will use the FAST Cache.

    The use of SAS Flash 3 type drives for the FAST Cache is not supported.

    The FAST Cache provides the following benefits:

    • Improved Total Cost of Ownership (TCO)

      The FAST Cache reduces the number of drive spindles needed for a given level of performance and allows you to replace high performance drives with more economical options. This is possible because the load on back-end hard drives is reduced. Because the FAST Cache copies the busy subsets of large storage capacities in 64 KB data chunks to Flash drives, the busiest areas of many LUNs or file systems use a small set of Flash drives. This allows a large set of slower, less expensive drives to deliver the performance typically provided by faster, more expensive drives. Over a period of time, pools with faster SAS drives can be replaced by new pools with slower NL-SAS drives, while maintaining the same application performance. This improves the financial (IOPS/dollar) and power (IOPS/KWH) efficiency of the storage system.

    • Reduced complexity

      At a system level, the FAST Cache helps make the most efficient use of Flash drive capacity. The FAST Cache does this by using Flash drives for the most frequently accessed data in the storage system instead of dedicating Flash drives to a particular application. It adjusts to a hot spot anywhere in the storage system, so that you do not need to analyze specific application requirements. It provides better performance to all applications in the storage system while using fewer Flash drives.

    • Highly scalable cache capacity

      The FAST Cache can scale up to a larger capacity than the maximum DRAM Cache capacity. This larger cache capacity means that all or a higher percentage of a customers working set can be promoted into the better performing FAST Cache. The working set is the most active part of an application.

    FAST Cache drive configurations

    The FAST Cache uses SAS Flash 2 drives configured in RAID 1 pairs. The drive sizes used to configure the FAST Cache and maximum FAST Cache capacity vary by model. For information, see the compatibility and interoperability documentation. Go to the support website to locate this documentation.

    You cannot mix drive types or sizes in the FAST Cache.

    FAST Cache actions

    You can expand or shrink the FAST Cache by adding or removing drives. You can also delete the FAST Cache, but this can impact system performance and the performance of pools currently using the FAST Cache. The FAST Cache deletion process takes time, because the storage system has to flush all of the cache data to the pool drives.

    FAST Cache best practices

    Use the FAST Cache under the following circumstances:

    • Large working sets of data must be stored and read, accessed frequently, and readily available. Regular (MCC) storage is not suitable for this type of data, because it is smaller and frequently flushed.
    • The system has enough disks for both data storage and performance improvement.

    For example, use the FAST Cache if the system has enough SAS Flash disks, is active with daily read/write transactions of big blocks of data, and is not used as stored long term storage for archival purposes that would be accessed on a weekly or monthly basis.

    Avoid using the FAST Cache for data that is sequential or that uses large-block I/O. For example, do not use the FAST Cache for database logs or circular logs, since their data is sequential.

    Create the FAST Cache

    Before you begin

    To create the FAST Cache, the FAST Cache license must be installed on the system and the system must have available SAS Flash 2 disks in sizes supported by the model. (See the compatibility and interoperability documentation for this information).

    Procedure
    1. Select the Settings icon, and then select Storage Configuration > FAST Cache.
    2. Select Create.
    3. Select the size and number of disks to use for the FAST Cache. The available disks are based on the number of available SAS Flash disks, spare disk policy, and system limits.
    4. Optionally, clear Enable FAST Cache for existing pools, if you do not want the FAST Cache enabled for all existing pools. You can enable the FAST Cache for individual pools at a later time.

    Enable or disable the FAST Cache for a pool

    Procedure
    1. Under Storage, select Pools.
    2. Select the relevant pool, and then select the Edit icon.
    3. On the General tab, select or clear Use FAST Cache.

    View system-level FAST Cache information

    Procedure
    1. Select the Settings icon, and then select Storage Configuration > FAST Cache to view the status, total space, and number of disks in the FAST Cache.
    2. Select the Settings icon, and then select Storage Configuration > FAST Cache Disks to view the name and size of each disk in the FAST Cache.

    View pool-level Fast Cache Information

    At the pool level, you can verify whether a specific pool is configured to use the FAST Cache.

    Procedure
    1. Under Storage, select Pools.
    2. Select the pool, and then select the Edit icon.
    3. On the General tab, view whether the Use FAST Cache field is enabled.

    Expand or shrink the FAST Cache capacity

    If you have a small FAST Cache, and your business's growth requires larger blocks of data to be read and written, you can expand the FAST Cache capacity by adding SAS Flash 2 drives.

    On rare occasions, you might want to shrink the FAST Cache capacity. For example, consider doing so under these circumstances:

    • The FAST Cache is too large for users' applications.
    • You need to repurpose some SAS Flash 2 drives to create storage pools with higher performance.
    • The storage system does not have enough slots left to be populated with additional disk drives for storage.
    Shrinking the FAST Cache can impact system performance and the performance of pools currently using the FAST Cache.
    Procedure
    1. Select the Settings icon, and then select Storage Configuration > FAST Cache.
    2. To expand the FAST Cache, select Expand. Then select the disks to add to the FAST Cache.
    3. To shrink the FAST Cache, select Shrink. Then select the disks to remove from the FAST Cache.

    Delete the FAST Cache

    Deleting the FAST Cache frees up disks for other uses. However, it can impact system performance and the performance of pools currently using the FAST Cache. The FAST Cache deletion process can take a long time, because it has to flush all of the cache data to the pool disks.
    Procedure
    1. Select the Settings icon, and then select Storage Configuration > FAST Cache.
    2. Select Delete.