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Re: 30 TB RAID6 + XFS slow write performance

To: John Bokma <contact@xxxxxxxxxxxxx>
Subject: Re: 30 TB RAID6 + XFS slow write performance
From: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>
Date: Tue, 19 Jul 2011 10:37:19 +0200
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4E24907F.6020903@xxxxxxxxxxxxx>
Organization: Intellique
References: <4E24907F.6020903@xxxxxxxxxxxxx>
Le Mon, 18 Jul 2011 14:58:55 -0500 vous écriviez:

> card: MegaRAID SAS 9260-16i
> disks: 14x Barracuda® XT ST33000651AS 3TB (2 hot spares).
> ~ 30TB

This card doesn't activate the write cache without a BBU present. Be
sure you have a BBU or the performance will always be unbearably awful.
Then proceed like Eric suggested. Initialize your filesystem with the
right options : su= your RAID stripe size, sw= your RAID array data
members (for RAID 6, the total number minus 2), don't forget the useful
option -l lazy-count=1, and mount with nobarriers and inode64.

BTW apparently you're confusing hot spares and parity drives. A RAID-6
array has 2 parity drives; then it may have or not 1 or more hot spares
(generally one is enough). I suppose your array is actually a 12 data +
2 parity drives.

Emmanuel Florac     |   Direction technique
                    |   Intellique
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