Date: Fri, 28 Jul 2017 15:56:11 +0500 From: "Eugene M. Zheganin" <emz@norma.perm.ru> To: freebsd-fs@FreeBSD.org Cc: freebsd-stable <freebsd-stable@FreeBSD.org> Subject: some general zfs tuning (for iSCSI) Message-ID: <8b41e7d6-7a2c-d456-2eee-93efd81aa86a@norma.perm.ru>
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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.
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