Martin,

To be very honest, I have no idea what the detailed specs are behind the disks 
(SAN).  This is an HP XP20000 disk system (Hitachi to be exact) filled with 
SATA disks.  I know that the way HP constructed this disk system (which is used 
by many other systems as well, next to all our DSSU Media Servers) as 1 large 
volume of which they give pieces to users who request some SAN disk space.  
This is not the way how it works on our other HP disk system (XP 12000 filled 
with fiber channel disks) but this system is only used for high critical 
applications.  And as you know, not many companies consider the backup 
environment as a critical application :-(

The 35-40 MB/sec for us is dramatic as we backup to these same disks with 
speeds up to 125 MB/sec.  So disks are filling up very rapidly.

Can you tell me what parameters you took to get your DSSU's up and running 
properly (disk block size, number of buffers and size of buffers on NBU side, 
...) ?

Best Regards,
Bart WALLEBROEK
Backup Admin & Systems & Applications Management & Support Specialist 
Enterprise Applications Delivery - Infrastructure Management

-----Original Message-----
From: Martin, Jonathan [mailto:JMARTI05 AT intersil DOT com] 
Sent: Friday, June 25, 2010 5:49 PM
To: WALLEBROEK Bart; veritas-bu AT mailman.eng.auburn DOT edu
Subject: RE: [Veritas-bu] Destaging going slow

Great.  I would say that is your "baseline", and that is just about what I get 
out of 15x1TB SATA disks in a Raid-5 at 8 streams. What kind of Raid controller 
are you using?  What kind of block sizes on that raid volume? What kind, and 
how many physical disks are in your raid set? Is this a SAN or DAS?  If it is a 
SAN, do you have other things on the same raid group? Are you using / what are 
your values in the touch files? Have you looked at your disk counters while the 
destaging is running? (Logical and Physical disk counters for individual 
disks.) Are you seeing high levels of disk queuing? Does your throughput to 
tape match the read/sec? 

35-40 MB/sec is not ideal, but I could consider it acceptable if you were using 
huge SATA disks. If you think you are not getting the performance you deserve 
from the hardware then I would suggest digging.  It took me two weeks to find 
the optimal settings that I run now.  In the mean time, don't listen to Ed.  
There are plenty of users on this forum who have DSSUs running just fine. I for 
one have something like 12 sites running DSSUs without issue.

-J

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