Date: Tue, 3 Oct 2017 17:03:18 +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: <A0EA3117-A40A-4163-AF84-76A08ABBFE4A@gmail.com> In-Reply-To: <caa120ab-5b88-8602-45b6-1fbbea9ad194@multiplay.co.uk> 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>
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> 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 Good catch then, thank you ! > 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. Yes this is also what I see. 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. Many thanks ! Ben
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