Omniback capacities

[Alan Riggs]

System:
OB 2.55
DLT7000 drive(s)
DLT IV tapes

Symptom:
No matter how I initialize a tape, I cannot get the expected amount of compressed data onto the volume. I have tried allowing Omniback to discover the size, which always results in a 20GB volume (yes, I know I can change this default). I have tried explicitely setting the value through the range from 40GB to 80GB. No matter what setting I use, the maximum amount of data I can write to a volume hovers around 30GB.

Hardware compression is set on the drive.

Has anyone seen this before? Is there a fix? I am using 6 tapes a night for backups, and it is annoying me.

[Rita C Workman]

Hi Alan,

You may be interested in what was discussed at this url...especially Andreas' comment..
http://my1.itrc.hp.com/cm/QuestionAnswer/1,1150,0x67d5f841489fd4118fef0090279cd0f9,00.html

I know for myself..and I am also OBII v2.55 on DLT7000 4/28. I always set the tape size to 70GB. I never let OBII decide, cause it will default to 20gb. I have managed to keep my backups to 3 tapes...and when I check the sizes and math, it is working with the 70gb.

I have just started upgrading systems to OBII 3.5...and I was amazed how simple it was. One down and about a dozen to go...
Regards,

[Andreas Voss]

Hi,

that sounds mistery. As i know OB writes to tape until it reaches the EOT no matter what the initial capacity was.
In my thought your poor capacity could be in case of not streaming (I/O to tape not sufficient for streaming). I've heard that in this case DLT drives changes to noncompressing mode to prevent huge start/stop events.
To verify this you could use the uncompress device (perhaps has to created) an use software compress by OB option.

Regards

[Alan Riggs]

Rita,
I can set the size to anything I want -- 20, 30, 50, 70, 80 GB. It makes no difference in the data that I can actually write to the tape. Media fills up between 29-31GB every time tested.

Andreas,
That is an interesting conjecture. I will do some playing, but I do not think that would be it. The drives in question are directly connected to the servers on dedicated SCSI paths. I would think it unlikely that the I/O streaming was insufficient.

[Rita C Workman]

Just a question.

On your drives...what is the segment size and block size set to?

[Alan Riggs]

Segment size 150. Block size "default"

[Rita C Workman]

Your segment is same as mine...my block is set to 128k.

I'm running out of places to look.....talk about frustrating..

Still looking though..

[Rita C Workman]

OOhhhh how frustrating...

My segment size is same...my block is 128k

Still looking...but running out of places I can think to check though..

ps...problems again with site...keep getting errors when I try to send this, so you may get this more than once. sorry.

[Alan Riggs]

No worries, Rita, I appreciate all help.

BTW -- I just noticed something interesting, the device drivers for this drive were not standard. The drivers 3m and c3t1d0BEST had a different digit immediately after the minor number. I have removed and recreated these drivers, perhaps that will make a difference.

[Rita C Workman]

OK.
Let me know if that works...you never know when you may run into this again somewhere..

Tx,

[Alan Riggs]

Well, reinstalling drivers had no noticeabel effect. Ran two full bacjups this weekend (oracle upgarde -- what fun). One rolled to second tape after 31574 MB, the other after 31581 MB.

Any one have a clue? I seem to be fresh out.

[Rita C Workman]

Hi Alan...boy I was really hoping those device files were the answer.

The only thing different from yours to mine is that block size. I think default is 64 and mine is set to 128. But I wouldn't think that would account for it....of course it does seem to be the last thing to try. Hey what have you got to lose??? Why not give it a try and then initialize a tape and give it a test...
Couldn't hurt...

I'll keep my eyes open, if I come across anything like this and let you know if I find something...

Let me know if you get it resolved....rworkman@wvbep.org, just in case...

Regards,