Hierarchical storage management (HSM) balance

The high-use and low-use data on each disk unit in the auxiliary storage pool (ASP) is redistributed. This action is done so that the high-use data resides on fast disk units and the low-use data resides on compression disk units, which are typically slower than standard disk units.

The ASP selected for a HSM balance must have a combination of compression disk units and non-compression disk units. You can only run a HSM balance following a trace ASP balance. The trace ASP balance function monitors the input/output (I/O) activity on each of the disk units in the ASP to determine where the high-use and low-use data resides.

Compression disk units have larger capacity, but are somewhat slower than non-compression disk units. This is due to the overhead of compression and decompression, and the variations in the length of the data that is written to disk. Typically, data that is found on disk units has a wide range of access requirements. The HSM balance function moves data that is accessed infrequently to compression disk units. Disk compression makes infrequently accessed data available online at a lower cost. System throughput improves when you move high-use data off of compression disk units. Moving the low-use data to the large compression disk units makes additional capacity available on the standard disk units so high-use data can be allocated.

The Start Auxiliary Storage Pool Balance (STRASPBAL) command is used to perform the HSM balance function. For example, if you want to run a HSM balance on ASP 4 for 25 minutes, enter the following command: STRASPBAL ASP(4) TYPE(*HSM) TIMLMT(25).

If you want to end a HSM balance before the time limit requested is reached, use the End Auxiliary Storage Pool Balance (ENDASPBAL) command. For example, if you want to end a running HSM balance on ASP 4, enter the following command: ENDASPBAL ASP(4).