Basic use case; utterly confused

[ Edited ]

Seems like a basic use case: take periodic backups from primary storage, and "vault" them to secondary, without continuing to consume space on primary.  Essentially, replace a tape backup system.

The problem with "normal" mirror/vault is that snapshots remain growing on the primary.  In our case they soon fill the primary, causing a production problem.  For a specific volume, I just want to take a monthly archival backup, and have it available for possible restore; I don't care about all the deltas during the month, which cause the snapshot to grow uncontrolled.

Support says there's no way, other than breaking the relationship after taking the copy.  But then we lose the ability to do anything with the backups if required.  Is there no way - e.g. powershell - others have found?

Getting rid of tape backup was a big selling point in getting us to buy a secondary system.  Yes, for MOST filesystems we're doing frequent snapmirrors, and accept that those snapshots must remain.  But if all I want in an occasional 100% copy of a volume...