High cache utilization on Dell EMC PowerMAX

The Commvault software uses EMC SMI-S to perform snapshot operations with the TimeFinder SnapVX engine. By default, for the mount operation, EMC SMI-S selects target devices. If it does not find free target devices, then it creates a new one. EMC SMI-S might end up creating 3-5 target devices per source volume. The more target devices, the higher the cache utilization. High cache utilization decreases the performance of the array. Recently, starting with the HYPERMAX OS 5977.810.184 version, the behavior of no-copy linked target devices changed. Even after unlinking, target devices contain snapshot data. If the unlinked snapshot gets deleted, the target device owns the snapshot delta. The EMC SMI-S provider can create up to 5 target devices per source LUN. This results in high number of target devices accumulated on the array and ends up higher allocation and cache utilization on array, which may significantly decrease the array performance. Commvault has introduced functionality to use a group of target devices. With this feature, only the defined group of pre-created linked devices can be used for snapshot mapping triggered by Commvault, thereby preventing excessive build-up of linked devices. To use this functionality, use the following snapshot properties:

Use SnapVX target devices from storage group: Specifies the storage group name from which SnapVX target devices can be selected.