Thanks for the good tips.
On another note, I have been told that the HP LTO3 drives will "scale
back" to LTO2 speeds if it detects the data feed is not fast enough to
drive the drive at LTO3 speed. Haven't tested this yet....but I know
this is one of the big features that is mentioned.
Thanks,
Kris
-----Original Message-----
From: veritas-bu-admin AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu] On Behalf Of
william.d.brown AT gsk DOT com
Sent: Tuesday, September 27, 2005 5:41 PM
To: veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] LTO3 Buffer Setting Recommendation - NEW
QUESTION
I don't have an immediate answer...asides from saying our policy is to
not buy LTO3 drives for now as we cannot see how we can stream them.
The MINIMUM data rate I'm told is ~40MB/s, below which they stop/start
and performance crashes.
Most of our disk systems don't come near that figure.
What I'd suggest is to do two things:
1) Use IOMeter to test the performance of the disks, and play
around
to see how they perform with one stream or several streams - you will
learn a lot about your disk subsystem, without having to run backups.
You may also want while doing that to investigate the HBA driver
settings for the disks, to make sure they are set to the vendor
recommendation. You may still want to experiment, as they are likely to
recommend 'typical'
settings, and pulling data off for backup may not be typical. Things
to
look at are the number of IO requests you can queue; the HBA vendor may
default to a number like 8 which is OK for tape but a disk array
(especially with a cache) may cope with 32 or even more. Of course if
these are the same HBAs that some application uses....you may have to go
carefully.
2) Use the -nocont option for bpbkar32 to run a backup that just
throws the data away, rather than sending it on to tape. You can then
see if your policies are hitting the limits of the disks. We spent a
lot of time trying to stream an LTO1 tape, and then found it was just
slow disks.
I'm not quite clear if you have the 4 disks on one disk HBA, or one HBA
per disk. I guess the former. If you can implement active/active
multipathing, you can double the performance in some cases - certainly
we see with our older HP EMA disks, that is what we get.
Defragment. Experiment with formatting the disk with the biggest block
sizes it will let you.
If you cannot stream the LTO 3, :-(. Try LTO2.....
William D L Brown
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