Date: Tue, 3 Oct 2017 09:31:50 +0200 From: Ben RUBSON <ben.rubson@gmail.com> To: Steven Hartland <steven@multiplay.co.uk>, 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: <1990B359-FC8D-4D6A-992B-7F77A07D83A6@gmail.com> In-Reply-To: <69fbca90-9a18-ad5d-a2f7-ad527d79f8ba@freebsd.org> References: <4A0E9EB8-57EA-4E76-9D7E-3E344B2037D2@gmail.com> <feff135a-3175-c5d0-eeb4-5639bb76789e@FreeBSD.org> <69fbca90-9a18-ad5d-a2f7-ad527d79f8ba@freebsd.org>
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> On 03 Oct 2017, at 09:25, Steven Hartland <steven@multiplay.co.uk> = wrote: >=20 > On 03/10/2017 07:12, Andriy Gapon wrote: >> On 02/10/2017 21:12, Ben RUBSON wrote: >>=20 >>> 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). >>>=20 >> 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? >>=20 >> Steve, what do you think? >>=20 > 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 ! Ben
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