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re[2]: xfsdump/xfsrestore questions.

To: Austin Gonyou <austin@xxxxxxxxxxxxxxx>
Subject: re[2]: xfsdump/xfsrestore questions.
From: Greg Freemyer <freemyer@xxxxxxxxxxxxxxxxx>
Date: Mon, 20 May 2002 18:53:27 -0400
Cc: <linux-xfs@xxxxxxxxxxx>
Organization: The NorcrossGroup
Sender: owner-linux-xfs@xxxxxxxxxxx
 
 >>  > If your data is 2:1 compressible, that is 7.2 GB/hr uncompressed. 
 >>  > That sounds like what you are getting on the windows box.
 >>  > 
 >>  The issue here is that both jobs are using compression, but Arcserve
 >>  2000 on NT is performing faster than say, tar or xfsdump. The problem
 >>  I've got with this though, is that it's so much longer there's got to be
 >>  something I could tweak, either with xfsdump or the drive, so that's
 >>  what prompted my query.

Tape drives slow down excessively when they go from a streaming to a 
non-streaming situation.

If your feedrate is borderline, then a small speed reduction in data throughput 
caused by the software, could have a huge impact on backup times.

 >>  > What sort of disk-drive speed do you have on the xfs box?  I'm sure
 >>  > you know that RAID can drastically improve your disk-speed.
 >>  10K RPM 18GB Seagate at LVD(80mb/s) (yes..I know about theoretical max,
 >>  etc.)
 >>  The HP is at 10MB/s, I'd prefer to make it 20MB/s though..at least.(can
 >>  set it in the SCSI bios I think?

That drive should be plenty fast, IIRC about 100 GB/hr if no seeks are involved.

For the HP, 7.2 GB/hr is only 2 MB/sec so the 10 MB/sec scsi bus should be fast 
enough unless your scsi bus is very busy doing other stuff.

Are your tape drive and disks sharing the same controller?  If so, the 
contention might be slowing things down just enough to kick you out of 
streaming.  If so, you would think it would happen under windows too.

Out of curiosity, if you do a xfsdump and send the output to /dev/null, what 
sort of time do you get?

As I said before, the general goal is to overdrive the tape by 3x, so if the 
tape can do a full backup in 90 minutes when it is streaming, the above needs 
to finish within 30 minutes to be optimum.

If the xfsdump time looks good, I would look into  scsi-bus contention between 
disk and tape.

BTW: I'm leaving for the day, and I won't be back on e-mail til wed., so maybe 
they above gives you something to chew on.

Greg

 >>  > BTW: With really high-end drives like SDLT (39 GB/hr compressed),
 >>  > you basically have to design your whole storage system around their
 >>  > required feed rate if you want them to be able to stream.
 >>  > 
 >>  I'm quite aware of that..but thanks for the reminder. :)

It's been a pain for me recently, so maybe I was a little pedantic.  

 >>  > Greg Freemyer
 >>  > Internet Engineer
 >>  > Deployment and Integration Specialist
 >>  > Compaq ASE - Tru64
 >>  > Compaq Master ASE - SAN Architect
 >>  > The Norcross Group
 >>  > www.NorcrossGroup.com
 >>  > 
 >>  > 

Greg Freemyer
Internet Engineer
Deployment and Integration Specialist
Compaq ASE - Tru64
Compaq Master ASE - SAN Architect
The Norcross Group
www.NorcrossGroup.com



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