Spanning tapes with DPM 2010

Regardless of how great disk back is, most administrators will want to do some regular off-site bound backups to tape and often the data can be larger than a single tape. Enter tape spanning, the ability to span a single back job over multiple tapes. This isn't best practice, but if you have a single 2TB resource and only a maximum capacity of 1.6TB per tape (LTO4) you don't have many options. Either you can purchase an expensive new tape drive with higher capacity or enable spanning.

Initially I was a little taken back by the absense of any tape spanning options in the DPM 2010 GUI, in fact even the official manuals have very little reference to how tape spanning can be done.

After some digging I found that spanning will in fact kick in by default if the protection group is larger than a single tape, but DPM will only wait 1 hour for a replacement tape until the job fails. This is more than enough time for a tape loader, but if your using a manual LTO drive this could be a problem.



The Solution

The solution lies in a simple registry key.

“HKLM\Software\Microsoft\Microsoft Data Protection Manager\1.0\Prompting”

Under this key is a REG_DWORD value named "PromptingTimeOut"

The value is in milliseconds, so for each hour you want to wait, you need to multiply your value by 3600000.

For example, 4 hours * 3600000 = 14400000

Be sure you enter the value as a decimal or your wait time might be totally different than what you were hoping.