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Note: that dynamic pools do not require dedicated hot spares. See the Dynamic Pools section for additional considerations.
When using traditional storage pools, Dell Unity automatically reserves 1 unbound drive out of every 31 drives of a given type for use as a hot spare. Note that hot spare drives have no special configuration, they simply remain unbound. Dell Unity will not allow a traditional storage pool to be created or expanded unless the available number of unbound drives is sufficient to create the requested pool and continue to satisfy the hot spare policy. Consider spare drive count requirements when designing traditional storage pool layouts.
Required hot spare count can be reduced by decreasing the number of individual drive types within the system. Table 1 illustrates this point—
| Drives for traditional storage pools | Total requires spare drives |
System 1 25TB usable | 9x 600GB SAS 15K 9x 1200GB SAS 10K 9x 1800GB SAS 10K | 3 total: 1x 600GB SAS 15K 1x 1200GB SAS 10K 1x 1800GB SAS 10K |
System 2 25TB usable | 27x 1200GB SAS 10K | 1 total: 1x 1200GB SAS 10K |
Note: that Dell Unity will throttle hot spare rebuild operations to reduce the impact to host I/O. Rebuilds will occur more quickly during periods of low system utilization.