Capacity saving and accelerated compression functions

The VSP G series and VSP F series storage systems provide the following functions to make efficient use of user capacity:

  • Capacity saving The capacity saving function includes data deduplication and data compression. Capacity saving enables you to reduce your bitcost for the stored data by deduplicating and compressing the data. Data deduplication and compression are performed by the controllers of the storage system. You can specify the post-process mode or inline mode to control when capacity saving processing occurs.
  • Accelerated compression The accelerated compression function enables you to reduce your bitcost for the stored data by allowing you to take advantage of the compression function in the FMC drives. Accelerated compression allows you to assign FMC capacity to a pool that is larger than the physical capacity of the FMC parity groups. The data access performance of the storage system is maintained when the accelerated compression function is used, as the compression engine is offloaded to the FMC drives.

The following table lists the combinations of applying accelerated compression and capacity saving and describes the functionality of each combination.

Combination

Functionality

Use only accelerated compression

Data compression is performed by the FMC drives. The storage controller does not perform the compression.

I/O performance is not affected because there is no overhead due to compression processing by the storage controller.

Use only controller-based compression

The storage controller compresses data and stores the compressed data in the pool. Use controller-based compression for drives other than FMC and for encrypted drives.

Using accelerated compression and controller-based compression at the same time results in compression being performed in the FMC drives only. Because of differences in storing and managing data by the storage controller, performance is lower than when only accelerated compression is used. Therefore, when accelerated compression can be enabled, you should use accelerated compression instead of controller-based compression. Use controller-based compression only when accelerated compression cannot be enabled.

Use accelerated compression and deduplication and compression

See Example 1 below

When multiple copies of identical data are stored in a pool, the storage controller keeps only one copy (deduplication). For compression, the storage controller detects that accelerated compression is enabled* and uses it instead of controller-based compression.

*Accelerated compression must be enabled for all parity groups in the pool.

Use deduplication and compression

See Example 2 below

The storage controller performs compression and deduplication processing. The storage controller has the largest overhead of the capacity saving processing.

Note
  • When BED encryption is not being utilized, use accelerated compression.
  • When accelerated compression is being utilized, do not enable controller-based compression.

Example 1: Applying deduplication (post-process mode) and accelerated compression

Example 2: Applying deduplication (post-process mode) and compression (capacity saving function)

Note
  • Saving Effect: If the capacity saving function is used, the saving ratio is calculated to include user data, meta data, and garbage data (that is generated by the system). If the data volume used capacity before the saving is smaller than the pool used capacity, the saving ratio might be lower and the saving capacity might be a hyphen (-) as an invalid value. If data in DP-VOLs are deleted by tasks such as those listed below, the saving ratio might be lower than you expected because the non-formatted data exists in FMC:
    • Deleting DP-VOLs
    • Formatting DP-VOLs
    • Initializing duplicated data in a pool
    For details about the formatted pool capacity or progress, see the item for Free + Reserved in the View Pool Management Status window.
  • Software Saving: If the capacity saving function is used, the saving ratio is calculated to include user data, meta data and garbage data (that is generated by the system). If the data volume used capacity before the saving is smaller than the pool used capacity, the saving ratio might be lower and the saving capacity might be a hyphen (-) as an invalid value. If you initialize the duplicated data in a pool, the saving effect might be different from what you expect until the LDEV format processing has completed. Therefore, only verify the saving effect after the duplicated data in a pool has finished initializing.
  • FMC Saving: If data in DP-VOLs are deleted by tasks such as those listed below, the saving ratio might be different from what you expect because the non-formatted data exists in FMC:
    • Deleting DP-VOLs
    • Formatting DP-VOLs
    • Initializing duplicated data in a pool
    For details about the formatted pool capacity or progress, see the item for Free + Reserved in the View Pool Management Status window.

Parent Topic
  • Dynamic Provisioning

    Thin provisioning is an approach to managing storage that maximizes physical storage capacity. Instead of reserving a fixed amount of storage for a volume, capacity from the available physical pool is assigned when data is actually written to the storage media.