Capacity balance
The capacity balance function rearranges the data on all of the disk units within an auxiliary storage pool (ASP).
The capacity balance moves data so that each disk unit has an equal percentage of used and unused space. This is useful when you add new units to an ASP. We want to avoid the situation where several disk units contain the majority of the data and the newly added disk units contain very little data. This situation leads to poor system performance. The balance function spreads the data in the ASP evenly across all of the disk units.
Below is a display which shows the effects of using capacity balance. Before using capacity balance the recently added Unit 4 contained very little data. The system storage management allocates newly created data to the disk unit that has the lowest percentage of capacity used. Thus, the system routes all new storage allocations to the unit 4. If the system uses that newly created data frequently, a potential bottleneck is created. The system directs all of the input/output (I/O) operations to a single disk unit instead of spreading it across all units in the ASP. The capacity balance performed on the ASP allows the data to be evenly distributed across all of the disk units in the ASP. This means that the distribution of future space allocation on the disk units in the ASP is even across all of the disk units in the ASP. That ensures that the I/O to those allocates are also evenly spread out amongst the disk units instead of being concentrated on the newly added disk unit.
| Unit | Before capacity balancing | After capacity balancing | ||
|---|---|---|---|---|
| Disk size | % used | Disk size | % used | |
| 1 | 1967 | 54.59% | 1967 | 55.69% |
| 2 | 1031 | 68.45% | 1031 | 55.80% |
| 3 | 1031 | 68.41% | 1031 | 55.76% |
| 4 | 1031 | 0.30% | 1031 | 55.77% |
To start capacity balance by a control language (CL) command use the Start
Auxiliary Storage Pool Balance (STRASPBAL) command. For example, if you want
to start a capacity balance on ASP 4 and have it run for 25 minutes, enter
the following command: STRASPBAL ASP(4) TYPE(*CAPACITY) TIMLMT(25).
If you want to end a capacity 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 capacity balance on ASP
4, enter the following command: ENDASPBAL ASP(4).