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Negligible improvement when using su/sw for hardware RAID5, expected?

To: xfs@xxxxxxxxxxx
Subject: Negligible improvement when using su/sw for hardware RAID5, expected?
From: Brian Davis <bridavis@xxxxxxxxxxx>
Date: Fri, 11 Aug 2006 23:10:29 -0400
Sender: xfs-bounce@xxxxxxxxxxx
User-agent: Thunderbird 1.5.0.5 (Windows/20060719)
Is this expected? I thought I would see more improvement when tweaking my su/sw values for hardware RAID 5.

Details, 3x300GB drives, 3Ware 7506-4LP Hardware RAID 5 using a 64K stripe size (non-configurable on this card).

FS creation and Bonnie++ results:

Untweaked:----------------------------------------------------------------------

localhost / # mkfs.xfs -f /dev/sda1
meta-data=/dev/sda1 isize=256 agcount=32, agsize=4578999 blks
       =                       sectsz=512   attr=0
data     =                       bsize=4096   blocks=146527968, imaxpct=25
       =                       sunit=0      swidth=0 blks, unwritten=1
naming   =version 2              bsize=4096
log      =internal log           bsize=4096   blocks=32768, version=1
       =                       sectsz=512   sunit=0 blks
realtime =none                   extsz=65536  blocks=0, rtextents=0
localhost / # mount -t xfs /dev/sda1 /raid
localhost / # cd /raid
localhost raid # bonnie++ -n0 -u0 -r 768 -s 30720 -b -f
Using uid:0, gid:0.
Writing intelligently...done
Rewriting...done
Reading intelligently...done
start 'em...done...done...done...done...done...
Version 1.93c ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP localhost 30G 27722 40 23847 37 98367 99 88.6 11 Latency 891ms 693ms 16968us 334ms

Tweaked:-------------------------------------------------------------------------

localhost / # mkfs.xfs -f -d sw=2,su=64k /dev/sda1
meta-data=/dev/sda1 isize=256 agcount=32, agsize=4578992 blks
       =                       sectsz=512   attr=0
data     =                       bsize=4096   blocks=146527744, imaxpct=25
       =                       sunit=16     swidth=32 blks, unwritten=1
naming   =version 2              bsize=4096
log      =internal log           bsize=4096   blocks=32768, version=1
       =                       sectsz=512   sunit=0 blks
realtime =none                   extsz=65536  blocks=0, rtextents=0
localhost / # mount -t xfs /dev/sda1 /raid
localhost / # cd /raid
localhost raid # bonnie++ -n0 -u0 -r 768 -s 30720 -b -f
Using uid:0, gid:0.
Writing intelligently...done
Rewriting...done
Reading intelligently...done
start 'em...done...done...done...done...done...
Version 1.93c ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP localhost 30G 27938 43 23880 40 98066 99 91.8 9 Latency 772ms 584ms 19889us 340ms


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