Date: Tue, 3 Oct 2017 17:07:33 +0200 From: Ben RUBSON <ben.rubson@gmail.com> To: Steven Hartland <steven@multiplay.co.uk>, FreeBSD-scsi <freebsd-scsi@freebsd.org>, Freebsd fs <freebsd-fs@FreeBSD.org> Cc: Andriy Gapon <avg@FreeBSD.org> Subject: Re: ZFS prefers iSCSI disks over local ones ? Message-ID: <49ADB654-E68B-4B88-AE8E-49F755092848@gmail.com> In-Reply-To: <A0EA3117-A40A-4163-AF84-76A08ABBFE4A@gmail.com> References: <4A0E9EB8-57EA-4E76-9D7E-3E344B2037D2@gmail.com> <feff135a-3175-c5d0-eeb4-5639bb76789e@FreeBSD.org> <69fbca90-9a18-ad5d-a2f7-ad527d79f8ba@freebsd.org> <9342D2A7-CE29-445B-9C40-7B6A9C960D59@gmail.com> <caa120ab-5b88-8602-45b6-1fbbea9ad194@multiplay.co.uk> <A0EA3117-A40A-4163-AF84-76A08ABBFE4A@gmail.com>
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> On 03 Oct 2017, at 17:03, Ben RUBSON <ben.rubson@gmail.com> wrote: >=20 >> On 03 Oct 2017, at 16:58, Steven Hartland <steven@multiplay.co.uk> = wrote: >>=20 >> On 03/10/2017 15:40, Ben RUBSON wrote: >>> Hi, >>>=20 >>> I start a new thread to avoid confusion in the main one. >>> (ZFS stalled after some mirror disks were lost) >>>=20 >>>=20 >>>> On 03 Oct 2017, at 09:39, Steven Hartland wrote: >>>>=20 >>>>=20 >>>>> On 03/10/2017 08:31, Ben RUBSON wrote: >>>>>=20 >>>>>=20 >>>>>> On 03 Oct 2017, at 09:25, Steven Hartland wrote: >>>>>>=20 >>>>>>=20 >>>>>>> On 03/10/2017 07:12, Andriy Gapon wrote: >>>>>>>=20 >>>>>>>=20 >>>>>>>> On 02/10/2017 21:12, Ben RUBSON wrote: >>>>>>>>=20 >>>>>>>> Hi, >>>>>>>>=20 >>>>>>>> On a FreeBSD 11 server, the following online/healthy zpool : >>>>>>>>=20 >>>>>>>> home >>>>>>>> mirror-0 >>>>>>>> label/local1 >>>>>>>> label/local2 >>>>>>>> label/iscsi1 >>>>>>>> label/iscsi2 >>>>>>>> mirror-1 >>>>>>>> label/local3 >>>>>>>> label/local4 >>>>>>>> label/iscsi3 >>>>>>>> label/iscsi4 >>>>>>>> cache >>>>>>>> label/local5 >>>>>>>> label/local6 >>>>>>>>=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. >>>>>>=20 >>>>> Note that local & iscsi disks are _exactly_ the same HDD (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). >>>>>=20 >>>> The output from gstat -dp on a loaded machine would be interesting = to see too. >>>>=20 >>> So here is the gstat -dp : >>>=20 >>> L(q) ops/s r/s kBps ms/r w/s kBps ms/w d/s kBps ms/d %busy Name >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da0 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da1 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da2 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da3 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da4 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da5 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da6 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da7 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da8 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da9 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da10 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da11 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da12 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da13 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da14 >>> 1 370 370 47326 0.7 0 0 0.0 0 0 0.0 23.2| da15 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da16 >>> 0 357 357 45698 1.4 0 0 0.0 0 0 0.0 39.3| da17 >>> 0 348 348 44572 0.7 0 0 0.0 0 0 0.0 22.5| da18 >>> 0 432 432 55339 0.7 0 0 0.0 0 0 0.0 27.5| da19 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da20 >>> 0 0 0 0 0.0 0 0 0.0 0 0 0.0 0.0| da21 >>>=20 >>> The 4 active drives are the iSCSI targets of the above quoted pool. >>>=20 >>> A local disk : >>>=20 >>> Geom name: da7 >>> Providers: >>> 1. Name: da7 >>> Mediasize: 4000787030016 (3.6T) >>> Sectorsize: 512 >>> Mode: r0w0e0 >>> descr: HGSTxxx >>> lunid: 5000xxx >>> ident: NHGDxxx >>> rotationrate: 7200 >>> fwsectors: 63 >>> fwheads: 255 >>>=20 >>> A iSCSI disk : >>>=20 >>> Geom name: da19 >>> Providers: >>> 1. Name: da19 >>> Mediasize: 3999688294912 (3.6T) >>> Sectorsize: 512 >>> Mode: r1w1e2 >>> descr: FREEBSD CTLDISK >>> lunname: FREEBSD MYDEVID 12 >>> lunid: FREEBSD MYDEVID 12 >>> ident: iscsi4 >>> rotationrate: 0 >>> fwsectors: 63 >>> fwheads: 255 >>>=20 >>> Sounds like then the faulty thing is the rotationrate set to 0 ? >>=20 >> Absolutely >=20 > Good catch then, thank you ! >=20 >> and from the looks you're not stressing the iSCSI disks so they get = high queuing depths hence the preference. >> As load increased I would expect the local disks to start seeing = activity. >=20 > Yes this is also what I see. >=20 > Any way however to set rotationrate to 7200 (or to a slightly greater = value (*)) as well for iSCSI drives ? > I looked through ctl.conf(5) and iscsi.conf(5) but did not found = anything related. Sorry, (*) or to a slightly lower value (of course...). I forgot to mention that as the initiator, target is a FreeBSD 11.0 = server. Ben
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