I've got 2012 DPM running a backup to an eSata drive. We will run an occasional test restore to an external USB drive and mount or boot the .VHD to verify functional backups. We've noticed a new USB drive will restore fine the first time. Three months later after trying to run a test restore to the same USB drive we get the error..."DPM cannot detect the volume f:\ on server SERVERNAME.domain.local. (ID: 31085) If the volume is present, this problem can be rectified by refreshing the state using the Get-Datasource -ProductionServer <ProductionServer> -Inquire cmdlet, then retry the current task."

Once we plug in a new USB drive we are able to restore...until we try to use this USB drive again three months later.

We are able to restore to the local RAID.

Hi,

This is a known problem, you can run the following SQL script to list volumes that are marked for deletion that have the drive letter of the removable drive.  Change the Server_name to your Server name hosting the USB drive, and change the F:\ to be the current drive letter of the removable USB drive.

Select * from  tbl_IM_Volume
Where serverid in (select Serverid from tbl_am_server AM where NetbiosName = 'server_name')
and VolumeLabel like '%F:\%'
and MarkedForDeletion = 1

You can then run the below script to unmark them for deletion and they should be available for a restore again.  Make a backup of the DPMDB before running this. 

update tbl_IM_Volume 
set MarkedForDeletion = 0
Where serverid in (select Serverid from tbl_am_server AM where NetbiosName = 'Server_name')
and VolumeLabel like '%F:\%'