Poor ext3 performance on RAID array

Rene Salmon rsalmon74 at gmail.com
Wed Aug 8 20:21:05 UTC 2007

Hi list,

I am having some strange performance issues with ext3 and I am hoping to
get some advice/hints on how to make this better.  First some background
on the setup.

We have a RAID 5 array 10+1+1 with one LUN.  That is 10 SATA drives one
parity drive and one dedicated spare.  The LUN is about 6.5TB.

Using a 2Gbit/sec fiber channel card I can do some dd writes to the raw
device and get speeds close to 200Mbytes/sec which is more or less the
max the card can do.

Next I create an xfs file system on the LUN and do a dd to xfs and get
speeds close to 150Mbytes/sec.

I want to use ext3 not xfs so next I put ext3 on the lun.  Now when I do
the dd to the ext3 lun I get 25-50Mbytes/sec depending on whether I have
the Raid controller cache turned on or off. Getting 50MBytes/sec with
the raid controller cache turned off.

I know that ext3 should perform better so I must be doing something
wrong.  Here is my mkfs.ext3

mkfs.ext3 -b4096 -Tlagefile4 /dev/dm-0

Thanks in advanced for any help on this.

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