Home > Storage > PowerMax and VMAX > Data Protection > Dell EMC PowerMax and VMAX All Flash: TimeFinder SnapVX Local Replication > Snapshot capacity usage
A single generation of a snapshot can never exceed the capacity of the source device at the time the snapshot was taken. A single generation of a snapshot could potentially use backend capacity equal to the source device usage at the time the snapshot was taken. However, the efficiency features in PowerMaxOS and HYPERMAX OS, such as thin provisioning, Data Reduction, and shared allocations, greatly reduce the amount of actual snapshot data in the system.
Snapshots can be terminated manually or set to self-expire through the time-to-live (TTL) option. Use of both methods together is the best way to ensure snapshot capacity is released timely. Manually terminating snapshots is recommended if the exact time of termination is an important factor for the environment. Setting an expiration date on every snapshot, including snapshots that will be manually terminated, is the best way to prevent snapshots from being forgotten and continuing to grow and consume system resources. Expiration is especially recommended if any level of automation is being performed to create snapshots, whether via script or Unisphere.
A snapshot that has a target linked cannot be terminated. This applies to manual termination and automatic expiration. Users should query the array for expired snapshots periodically to verify that there are no targets linked preventing termination.
Resources consumed by snapshots that were created by other solutions such as ProtectPoint, RecoverPoint, and AppSync also need to be monitored. Pausing use of those applications without performing proper snapshot cleanup may consume valuable system resources.
When snapshots are terminated, the underlying cleanup process is a lower priority task designed to give priority to other operations in the array, like host I/O for example. This ensures that snapshot termination will not affect performance of the devices involved or performance of the system. The rate at which snapshot capacity will be freed depends available system resources. Therefore, the rate may vary across systems, and may even vary on a single system during different periods of activity.