Veritas-bu

[Veritas-bu] 6.0 DSSU Behavior

2007-01-26 16:03:01
Subject: [Veritas-bu] 6.0 DSSU Behavior
From: BBahnmiller at pier1.com (Bahnmiller, Bryan)
Date: Fri, 26 Jan 2007 15:03:01 -0600
  I did some extensive testing trying to figure out tuning for DSSU's
and LTO2/LTO3 tape drives. The testing was done on an IBM p5 520 lpar, 4
GB RAM, 2 2Gb/s FC HBA, 1 Gb/s nic. The disk I tested against were a 3
letter major vendor medium range ATA array, medium range FC array, and
high end FC array.

  The interesting thing I found was that destaging from a DSSU was
significantly slower than writing those same files to tape using a
regular backup process. If I recall, destaging was about 50% - 70% the
speed of a tape backup. I tried many different fragment sizes to no
avail. The destaging process evidently has a lot of overhead involved
that slows down the tape write process.

Bryan

_______________________________

        From: veritas-bu-bounces at mailman.eng.auburn.edu
[mailto:veritas-bu-bounces at mailman.eng.auburn.edu] On Behalf Of
Karl.Rossing at federated.ca
        Sent: Wednesday, January 24, 2007 2:46 PM
        To: Martin, Jonathan (Contractor)
        Cc: veritas-bu at mailman.eng.auburn.edu;
veritas-bu-bounces at mailman.eng.auburn.edu
        Subject: Re: [Veritas-bu] 6.0 DSSU Behavior
        
        

        My comments are below but i thought that I'd start with my
config. 
        
        Sun V240 Solaris 10 Master/Media(There is only one) 
        4GB of Ram 
        Dual 1.5Ghz 
        Two scsi LTO2 Autloaders. 
        Each Autoloader has one LTO2 drive. 
        Each autoloader is on a separate LVD channel. 
        1 dual port 2Gig fibre channel card. 
        One Gigbit Ethernet SX Fibre Card 
        The SAN has four 2GB fibre channel ports. 
        
        veritas-bu-bounces at mailman.eng.auburn.edu wrote on 01/24/2007
02:10:58 PM:
        
        > What are the advantages / disadvantages of assigning multiple
DSSUs to
        > the same volume?
        
        Slow speed. What i have done is connect each DSSU to it's own
Fibre Channel Port. This way i can (in theory) get 60MB/Sec per port.
This was done on Solaris and I only have two DSSU's. 
        
        I have to say that i did not bench mark 1 volume for two dssu's.
It might be beneficial to run a bkkar32 on the DDSU to see how fast you
can pull data off. 
        
        > Example - I've got a 2TB volume on a media server (/array or
E:\) that
        > has two folders on it, DSSU1 and DSSU2.  Both are configured
with a 98%
        > High Water Mark and 80% Low Water Mark (defaults.)
        
        The issue that I'm having with the high water mark is that
Solaris doesn't delete the data fast enough. So for the time being, i
have dropped the high water mark to 90%. 
        
        I also try to make my DSSU's 1.5x larger than one nightly
backup. This way, if i have tape drive issues, i can deal with them in
the morning. 
        
        <bitch> 
        One things that bugs me is that the "final destination volume
pool". If i want to move data to a different volume pool, I have to
change it and remember to set it back to my daily. For the time being
I'm sending my monthend data to the drive directly. Shoe shinning be
damned. 
        </bitch>



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