Re: 30 TB RAID6 + XFS slow write performance

Emmanuel Florac
2011-07-19T08:37:37Z

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).
> RAID6
> ~ 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.

regards,
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