Summary - I removed the majority of content from a file server, and now most of my backups are gone. I was using Windows Server Backup to a USB 2TB HD.
A backup occurred without error on 1/19/2013 at 11:00PM.
On 1/20/2013, I had the following drive configuration on my SBS 2011 server:
c: 1T
d: 2T
e: 2T
f: 2T
Drive c: was system files (~500G used), d: was Exchange (~ 100G used), e: was files (~400G), f: was backups and was not backed up.
I reconfigured the drives so that I had:
c: 1T
d: 2T
The others moved their content to other servers, were removed, and repurposed.
A backup occurred 1/20/2013 at 11:00 PM with warnings that some drives were not available.
On the morning of 1/21/2013, I accessed the backup from 1/19 in order to restore some files from e: that were not transferred. At that time, there were > 20 or so backup copies.
In order to clear the warning, I changed the backup to exclude e:.
The server backed up successfully at 11:00 PM on 1/21/2013.
At about 4:00 PM on 1/22/2013, I checked the backup again to restore another set of files, and saw that there was now only one backup set available - the one from 1/20/2013.
It seems that somehow, by removing e: from the backup set, SBS reset the history and also removed those files from the restore set. My understanding of how the available backups were kept was that as the amount of change increased enough to require more space than was available on the drive, copies were released on a FIFO basis in order to free space. In that case, the amount of data being backed up decreased substantially. In fact, one backup (with warnings due to the now missing e:) occurred after the drive change and a restore happened after that point as well. The key thing seems to be removing the e: from the backup set.
I tend to thing that the data from the previous backups is still on the drive, but that the index is going. Is there ANY way I can recover data from a backup made that is no longer listed from the recover choices? The files that I need were on the (now re-purposed and reformatted) e:.
For reference, the destination usage shows 1 copies, 1863 GB capacity, 889 GB used space. The total data being backed up is about 624 GB.
There is not a rotating backup or other known backup.