We’ve recently had a few questions about the auto-delete functionality in Windows Server 2008 Backup. As described in my article on Windows Server Backup, it deletes old versions of backups as required.
However, we’ve had reports where the auto-delete function isn’t working. That is, the backups work for several days, fill up the disk, and then fail.
I’ve since found out that the auto-delete feature deletes the older version of backups on the disk by deleting the corresponding shadow copy on the backup device.
However, the auto-delete feature does not automatically delete backups if space utilization by older copies is less than 1/8 of the disk size (12.5%). That means if the one full backup copy does not fit in the 7/8 of the disk size, backup may fail with disk full error (0x80780030 media is full error).
We recommend that users encountering this problem upgrade to a bigger backup disk.
Hope this helps!