On Sep 7, 2009, at 1:32 AM, James Lever <j@xxxxxxxxxxxx> wrote:
On 07/09/2009, at 10:46 AM, Ross Walker wrote:
zpool is RAIDZ2 comprised of 10 * 15kRPM SAS drives behind an LSI
1078 w/ 512MB BBWC exposed as RAID0 LUNs (Dell MD1000 behind PERC
6/E) with 2x SSDs each partitioned as 10GB slog and 36GB remainder
as l2arc behind another LSI 1078 w/ 256MB BBWC (Dell R710 server
with PERC 6/i).
This config might lead to heavy sync writes (NFS) starving reads
due to the fact that the whole RAIDZ2 behaves as a single disk on
writes. How about a 2 5 disk RAIDZ2s or 3 4 disk RAIDZs?
Just one or two other vdevs to spread the load can make the world
This was a management decision. I wanted to go down the striped
mirrored pair solution, but the amount of space lost was considered
too great. RAIDZ2 was considered the best value option for our
Well a MD1000 holds 15 drives a good compromise might be 2 7 drive
RAIDZ2s with a hotspare... That should provide 320 IOPS instead of
160, big difference.
The system is configured as an NFS (currently serving NFSv3),
iSCSI (COMSTAR) and CIFS (using the SUN SFW package running Samba
3.0.34) with authentication taking place from a remote openLDAP
There are a lot of services here, all off one pool? You might be
trying to bite off more then the config can chew.
Thatâs not a lot of services, really. We have 6 users doing builds
on multiple platforms and using the storage as their home directory
(windows and unix).
Ok, six users, but what happens during a build?
The issue is interactive responsiveness and if there is a way to
tune the system to give that while still having good performance for
builds when they are run.
Look at the write IOPS of the pool with the zpool iostat -v and look
at how many are happening on the RAIDZ2 vdev.
Try taking a particularly bad problem station and configuring it
static for a bit to see if it is.
That has been considered also, but the issue has also been observed
locally on the fileserver.
Then I suppose you have eliminated automounter as a culprit at this
That doesn't make a lot of sense to me the L2ARC is secondary read
cache, if writes are starving reads then the L2ARC would only help
I was suggesting that slog write were possibly starving reads from
the l2arc as they were on the same device. This appears not to have
been the issue as the problem has persisted even with the l2arc
devices removed from the pool.
The SSD will handle a lot more IOPS then the pool and L2ARC is a lazy
reader, it mostly just holds on to read cache data.
It just may be that the pool configuration just can't handle the
write IOPS needed and reads are starving.
Possible, but hard to tell. Have a look at the iostat results Iâve
The busy times of the disks while the issue is occurring should let
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