DP 3.5 sp2 LTO-4 tapes not writing as much data as they should

[Rui_bikini]

Hello guys

I have been running DP 3.5sp2 for about 2 years, to make tapes that are a single job per tape. Basically, I fill up a folder with files resulting from archiving my projects until I have about 750GB, and then lay it as a single job, all at once to an LTO-4, and that's it, I'll only run that tape again to restore if I need to.

The thing is that recently, I haven't been able to write the 750GB to a tape. It will "fill up" randomly at anywhere between 550 to 650GB, and a backup job ends up failing at least once. Normally I erase that tape, try it again and, if I'm lucky it'll actually work out. When it does, the log file shows somethign like :

"Completed  - 620GB

Native capacity - 780GB

Remaining - 40GB"

So, what happened to those "extra" 120GB?

This is very random, I have been trying to defend myself by deciding to backup when I have about 600/650GB of files, but still sometimes it fails 1GB away from completion.

Does anyone have any idea why this happens?

Thanks in advance

[Dennis Handly]

If compression is involved, it depends on what you compress.

Otherwise if you don't supply the data fast enough, you may be wasting tape space.

[Lpolling]

Could it be really a slow stream filling blank space on a disk?  I know I've personally seen my stream dip to slow rates and fill tapes just fine.  The files being backed up are already compressed on the server, but Software and Hardware compression is turned on by default. 

Im currently having the same problem with DP 3.5 SP2 using 1/8 storageworks autoloader LTO3.  Tape is only filling up to 60% capacity before moving onto the next tape.  DP is showing that remaining native capacity is 1-2gb per tape. 

ALSO found this artical that refernaces DP express but a newer version.  The artical is mainly about DPM 2010 not filling up tapes but it is an intersting concept.  Sort of what Dennis eluded to but not in the way of writing blank tape but I/O errors causing DP to give false "tape full" reports.  DP is referanced twards the bottom, i've clipped the info in to this post below.

Whole Post:

http://social.technet.microsoft.com/Forums/en-US/dpmtapebackuprecovery/thread/e718e8e6-c0d6-496e-9407-ea1ccf51bb98

Clipped section:

Philip Harrison

Infinite Technology

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Just a quick update on this.  I spoke to HP again, they denied strongly that the problem was there's, claimed DPM incompatibilities with the drive etc etc.  They finally had me try their Data Protector; it was showing errors after a few gig of backing up to the tape!  Suddenly they suggested I try creating the registry key

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\SCSI\Sequential&Ven_HP&Prod_Ultrium_4-SCSI\6&c0db181&0&000300\Device Parameters\Storport]
"BusyRetryCount"=dword:0000004b

Rebooted the server and ran 'writeforspanning' again, now it gets to tape position 12420080, which is 758Gb which I imagine is correct for a 800/1600Gb tape.  Running it again now to be sure, but it's never got that far before so that might be it!

• Proposed As Answer by Gai-jin Tuesday, January 11, 2011 7:43 PM
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