Best Practices for Managing Physical Space on FlashSystems 900-AE3

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Best Practices for Managing Physical Space

IBM FlashSystem 900 Model AE3 and V9000 Model AE3 have built-in hardware compression. These systems allow users to overprovision volumes up to the maximum logical capacity. The ratio between the logical data written to the system (effective capacity) and physical capacity consumed (usable capacity) is the compression ratio. Planning and monitoring are key to avoid running out of physical space.

Planning:

While an average compression ratio of 2:1 is typical, some data will compress better and some data will not compress, such as encrypted data and already compressed data. The best way to estimate space utilization is to run Comprestimator on the data set before migrating it to the FlashSystem.

If the compressibility of the data is unknown, the system should be configured based on a conservative estimate of the compression ratio or the physical capacity only. It is not recommended that you exceed 85% of physical capacity.

When AE3 is part of FlashSystem V9000 or virtualized behind SVC/Storwize:

Do not configure AE3 as a single large mdisk (this was how V9000 AE2 was configured). Configure 8 mdisks for best performance.

Monitoring:

To avoid running out of physical space on the system, the useable capacity should be carefully monitored on the GUI of the AE3. The AE3 GUI is the only capacity dashboard that shows the physical capacity. The virtualization layer (Storwize/SVC/V9000) will only show the effective capacity of the AE3 and will not provide physical space warnings for the AE3 system. Monitoring is especially important when migrating large amounts of data onto the AE3.

IBM strongly encourages users to configure Call Home on the AE3. Call Home monitors the physical free space on the system and will automatically open a service call for systems that reach 92% of their useable capacity.

The AE3 GUI will also issue warnings as the system starts to run out of capacity:

When AE3 is part of FlashSystem V9000 or virtualized behind SVC/Storwize:

Spectrum Virtualize v8.1 added unmap support which allows users to free up space on backend storage. V8.1.x is the minimum level for V9000 and is strongly recommended for SVC/Storwize when virtualizing AE3.

FlashSystems with Hardware Compression               

9840-AE3 FlashSystem 900

9843-AE3 FlashSystem 900              

9846-AE3 FlashSystem V9000

9848-AE3 FlashSystem V9000                      

A more detailed best practices guide is available at http://www.ibm.com/support/docview.wss?uid=ibm10735459