Implications of Removing a Cell from an Instant Capacity System
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The Instant Capacity software tracks the expected number of inactive components (cores, cells, and memory) in a complex and knows the actual number of active and inactive components. The complex is in compliance if the actual number of inactive components meets or exceeds the expected number of inactive components.
The complex is out of compliance if the actual number of inactive components is less than the expected number of inactive components and no temporary capacity exists.
However, a complex can also get out of compliance if a cell is removed from the complex. For example, if a cell contains inactive cores that are contributing to compliance, and the cell is removed, there will be fewer inactive cores on the complex. This may result in the complex being out of compliance and temporary capacity may begin to be debited.
Example A-1 Removing a Cell and Decreasing the Actual Number of Inactive Cores
For example, a complex contains two cells, with two partitions having two inactive and two active cores each. The Instant Capacity software expects the complex to have four inactive cores. If one of the cells (0) experiences a hardware problem, and you remove the cell, the complex is left with only one cell that contains two active and two inactive cores. The complex is now out of compliance because four inactive cores are expected to be in the complex, yet there are only two inactive cores.
Table A-1 Removing a Cell — Decrease Inactive Cores
State | Partition (Cell) 0 | Partition (Cell) 1 | Notes |
|---|---|---|---|
Before Cell 0 is Removed | 2 active | 2 active | 4 inactive cores expected (in compliance) |
After Cell 0 is Removed | 0 active | 2 active, 2 inactive | 4 inactive cores expected (out of compliance) |
In the above example, all cores in the removed cell are assumed to be active. This causes the complex to be out of compliance as the complex has two more active cores than it has core usage rights. This results in the complex consuming two hours of temporary capacity for each hour that the complex remains in this state. Deactivating another core from Cell 1 decreases the amount of temporary capacity being consumed, but since at least one core must be active per active cell, this complex cannot remain in compliance except through the use of temporary capacity.
Note that removal of a cell, followed by a reboot of the affected partition, does not affect the intended active number for the partition, or the required number of inactive cores which is determined by the overall availability of core usage rights across the complex. During the period when the cell is absent, temporary capacity may be consumed if the number of inactive cores is less than the expected number of inactive cores. Having additional Temporary Instant Capacity allows this system to remain in compliance even in the presence of a cell hardware failure.