Snapshot retention and snapshot rules

Snapshot Administration Guide for Hitachi NAS Platform

Part Number

Snapshot rules are configured with a queue size which determines the maximum number of snapshots to keep. When this number is reached, the queue is considered full. Taking a snapshot using a snapshot rule when its queue is full will apply a Queue-Full policy associated with this rule. The supported policies are:
  • MoveOutOfQueueAndDelete

    The oldest snapshot will be moved out of the queue and will be either be scheduled for deletion if it is retained or deleted immediately if it is not retained. When using this policy, it is important to avoid taking snapshots faster than they are deleted. Such a configuration will lead to exceeding the file system limit on the number of snapshots (1024), or running out of space. Ideally, retention interval should be less than the queue depth multiplied by the interval at which snapshots are taken. For example, if a snapshot schedule is configured to take snapshots hourly and the queue depth is 24, retention should be set to less than 24 hours. In this case, when a new snapshot is to be taken and the queue is full, the oldest snapshot in the queue will have its retention expired and hence will be deleted immediately.

    If not explicitly set, this is the policy that will be applied.

  • IgnoreRetentionAndDelete

    The oldest snapshot will be moved out of the queue and deleted immediately, even if it is retained.

  • StopCreatingNewSnapshots

    It will not be possible to take a new snapshot if the oldest snapshot in the queue is retained and until its retention expires.