Dell Technologies recommends including a Flash tier in a hybrid pool where snapshots will be active.
Be aware that snapshots increase the overall CPU load on the system and increase the overall drive IOPS in the storage pool. Snapshots also use pool capacity to store the older data being tracked by the snapshot, which increases the amount of capacity used in the pool, until the snapshot is deleted. Consider the overhead of snapshots when planning both performance and capacity requirements for the storage pool.
Before enabling snapshots on a storage object, it is recommended to monitor the system and ensure that existing resources can meet the additional workload requirements (refer to the Hardware Capability Guidelines section, Table 2). Enable snapshots on a few storage objects at a time, and then monitor the system to be sure it is still within recommended operating ranges, before enabling more snapshots.
It is recommended to stagger snapshot operations (creation, deletion, etc.). This can be accomplished by using different snapshot schedules for different sets of storage objects. It is also recommended to schedule snapshot operations after any FAST VP relocations have completed.
Snapshots are deleted by the system asynchronously; when a snapshot is in the process of being deleted, it will be marked “Destroying”. If the system is accumulating “Destroying” snapshots over time, it may be an indication that existing snapshot schedules are too aggressive; taking snapshots less frequently may provide more predictable levels of performance.
Note that Dell Unity will throttle snapshot delete operations to reduce the impact to host I/O. Snapshot deletes will occur more quickly during periods of low system utilization.