Date: Tue, 3 Oct 2017 08:39:36 +0100 From: Steven Hartland <steven@multiplay.co.uk> To: Ben RUBSON <ben.rubson@gmail.com>, Andriy Gapon <avg@FreeBSD.org> Cc: Freebsd fs <freebsd-fs@FreeBSD.org>, FreeBSD-scsi <freebsd-scsi@freebsd.org> Subject: Re: ZFS stalled after some mirror disks were lost Message-ID: <9bce89eb-4d6f-aec1-df44-ebf794a3123b@multiplay.co.uk> In-Reply-To: <1990B359-FC8D-4D6A-992B-7F77A07D83A6@gmail.com> References: <4A0E9EB8-57EA-4E76-9D7E-3E344B2037D2@gmail.com> <feff135a-3175-c5d0-eeb4-5639bb76789e@FreeBSD.org> <69fbca90-9a18-ad5d-a2f7-ad527d79f8ba@freebsd.org> <1990B359-FC8D-4D6A-992B-7F77A07D83A6@gmail.com>
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On 03/10/2017 08:31, Ben RUBSON wrote: >> On 03 Oct 2017, at 09:25, Steven Hartland <steven@multiplay.co.uk> wrote: >> >> On 03/10/2017 07:12, Andriy Gapon wrote: >>> On 02/10/2017 21:12, Ben RUBSON wrote: >>> >>>> A sustained read throughput of 180 MB/s, 45 MB/s on each iscsi disk >>>> according to "zpool iostat", nothing on local disks (strange but I >>>> noticed that IOs always prefer iscsi disks to local disks). >>>> >>> Are your local disks SSD or HDD? >>> Could it be that iSCSI disks appear to be faster than the local disks to the >>> smart ZFS mirror code? >>> >>> Steve, what do you think? >>> >> Yes that quite possible, the mirror balancing uses the queue depth + rotating bias to determine the load of the disk so if your iSCSI host is processing well and / or is reporting non-rotating vs rotating for the local disks it could well be the mirror is preferring reads from the the less loaded iSCSI devices. > Note that local & iscsi disks are _exactly_ the same (same model number, same SAS adapter...). > So iSCSI ones should be a little bit slower due to network latency (even if it's very low in my case). > Once production back, after having analysed the main issue of this thread, I should then > try to find whether or not iSCSI disks are seen as rotating disks. > > Thanks for the hint ! Hmm, the output from gstat -dp on a loaded machine would be interesting to see too. Regards Steve
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