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<tt>An Slog (you wrote ZIL but you meant Slog as ZIL is onpool
logging while Slog is logging on a dedicated device) is not a
write cache. It's a logging feature when sync write is enabled and
only read after a crash on next bootup. </tt><tt>CIFS does not
use sync per default and for NFS (that wants sync per default) you
can and should disable when you use NFS as a pure backup target.
Your benchmarks clearly show that sync is not enabled otherwise
write performance with a large vdev would be more like 30-50 MB/s
instead your 400-700 MB/s. <br>
<br>
If you want to enable sync, you should look at Intel Optane as
Slog as this is far better than any other Flash based Slog.</tt><tt><br>
</tt><tt><br>
</tt><tt>ZFS use RAM as read and write cache. The default write
cache is 10% of RAM up to 4GB so the first option to improve write
(and read) performance is to add more RAM. A fast L2Arc (ex Intel
Optane, size 5-max 10x RAM) can help if you cannot increase RAM or
if you want a read ahead functionality that you can enable on an
L2Arc. Even write performance is improved with a larger read cache
as even writes need to read metadata.</tt><tt><br>
</tt><tt><br>
</tt><tt>Beside that, I would not create a raid Zn vdev from 24
disks. I would prefer 3 vdevs from 8 disks or at least two vdevs
from 12 disks as pool iops scale with number of vdevs.</tt><tt><br>
</tt><tt><br>
</tt><tt><br>
</tt><tt>Gea</tt><tt><br>
</tt><tt>@napp-it.org</tt><br>
<br>
<div class="moz-cite-prefix">Am 18.06.2018 um 08:50 schrieb
priyadarshan:<br>
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<pre wrap="">On 18 Jun 2018, at 08:27, Oliver Weinmann <a class="moz-txt-link-rfc2396E" href="mailto:oliver.weinmann@icloud.com"><oliver.weinmann@icloud.com></a> wrote:
Hi,
we have a HGST4u60 SATA JBOD with 24 x 10TB disks. I just saw that back then when we created the pool we only cared about disk space and so we created a raidz2 pool with all 24disks in one vdev. I have the impression that this is cool for disk space but is really bad for IO since this only provides the IO of a single disk. We only use it for backups and cold CIFS data but I have the impression that especially running a single VEEAM backup copy job really maxes out the IO. In our case the VEEAM backup copy job reads and writes the data from the storage. Now I wonder if it makes sense to restructure the Pool. I have to admit that I don't have any other system with a lot of disk space so I can't simply mirror the snapshots to another system and recreate the pool from scratch.
Would adding two ZIL SSDs improve performance?
Any help is much appreciated.
Best Regards,
Oliver
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Hi,
I would be interested to know as well.
Sometimes we have same issue: need for large space vs need to optmise for speed (read, write, or both). We also are using, at the moment, 10TB disks, although never do RAID-Z2 with more than 10 disks.
This page has some testing that was useful to us: <a class="moz-txt-link-freetext" href="https://calomel.org/zfs_raid_speed_capacity.html">https://calomel.org/zfs_raid_speed_capacity.html</a>
Section «Spinning platter hard drive raids» has your use case (although 4TB, not 10TB):
24x 4TB, 12 striped mirrors, 45.2 TB, w=696MB/s , rw=144MB/s , r=898MB/s
24x 4TB, raidz (raid5), 86.4 TB, w=567MB/s , rw=198MB/s , r=1304MB/s
24x 4TB, raidz2 (raid6), 82.0 TB, w=434MB/s , rw=189MB/s , r=1063MB/s
24x 4TB, raidz3 (raid7), 78.1 TB, w=405MB/s , rw=180MB/s , r=1117MB/s
24x 4TB, striped raid0, 90.4 TB, w=692MB/s , rw=260MB/s , r=1377MB/s
Different adapters/disks will change the results, but I do not thing ratio will change much.
It would be interesting to see how ZIL would affect that.
Priyadarshan
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