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extremely slow write performance plaintext

To: xfs@xxxxxxxxxxx
Subject: extremely slow write performance plaintext
From: Cory Coager <ccoager@xxxxxxxxxxxxxxx>
Date: Thu, 13 Jan 2011 16:22:36 -0500
Banner: Set
Organization: Davis Vision
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101208 Lightning/1.0b2 Thunderbird/3.1.7
Hardware is 2x 2.6ghz cpu, 6gb RAM, 2 SAS arrays consisting of 24 drives in hardware RAID 6, 5.87tb total. The two arrays were added to a volume group and multiple logical volumes were created. I am getting over 180MB/s read speeds and 40MB/s write speeds on all the LV's except one. One of the LV's is getting ~1MB/s write speeds, however read speeds are fine. There are NO snapshots.

meta-data=/dev/mapper/vg0-shared isize=1024 agcount=32, agsize=17616096 blks
         =                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=563715072, imaxpct=25
         =                       sunit=0      swidth=0 blks, unwritten=1
naming   =version 2              bsize=4096
log      =internal               bsize=4096   blocks=32768, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

# dd if=/dev/zero of=zero bs=1k count=1048576
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 2089.95 seconds, 514 kB/s

# dd if=zero of=/dev/null bs=1k
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 4.70878 seconds, 228 MB/s

Any idea what is wrong with this and how to fix it?

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