When Unitrends creates snapshots, it copies the snap shots to the Unitrends storage and then deletes the snapshot. If the delete operation fails, then every time Unitrends creates a snapshot the snapshot chain will grow in size. The snapshot chain has a maximum size of 30 snapshots. After the 30th snapshot no more can be created. The error, “Snapshot chain is too long” will appear in the Unitrends logs. You will also not be able to create a snapshot in XenCenter or from an xe command