On Fri, 28 Jul 2017 12:56:11 +0200, Eugene M. Zheganin <e...@norma.perm.ru>
wrote:
Hi,
I'm using several FreeBSD zfs installations as the iSCSI production
systems, they basically consist of an LSI HBA, and a JBOD with a bunch
of SSD disks (12-24, Intel, Toshiba or Sandisk (avoid Sandisks btw)).
And I observe a problem very often: gstat shows 20-30% of disk load, but
the system reacts very slowly: cloning a dataset takes 10 seconds,
similar operations aren't lightspeeding too. To my knowledge, until the
disks are 90-100% busy, this shouldn't happen. My systems are equipped
with 32-64 gigs of RAM, and the only tuning I use is limiting the ARC
size (in a very tender manner - at least to 16 gigs) and playing with
TRIM. The number of datasets is high enough - hundreds of clones, dozens
of snapshots, most of teh data ovjects are zvols. Pools aren't
overfilled, most are filled up to 60-70% (no questions about low space
pools, but even in this case the situation is clearer - %busy goes up in
the sky).
So, my question is - is there some obvious zfs tuning not mentioned in
the Handbook ? On the other side - handbook isn't much clear on how to
tune zfs, it's written mostly in the manner of "these are sysctl iods
you can play with". Of course I have seen several ZFS tuning guides.
Like Opensolaris one, but they are mostly file- and
application-specific. Is there some special approach to tune ZFS in the
environment with loads of disks ? I don't know.... like tuning the vdev
cache or something simllar. ?
Thanks.
Eugene.
What version of FreeBSD are you running?
What is the system doing during all this?
How are your pools setup (raidz1/2/3, mirror, 3mirror)?
How is your iSCSI configured and what are the clients doing with it?
Is the data distributed evenly on all disks?
Do the clients write a lot of sync data?
I think this kind of information helps people helping you.
Regards,
Ronald.
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