Date: Tue, 3 Oct 2017 16:40:17 +0200 From: Ben RUBSON <ben.rubson@gmail.com> To: Freebsd fs <freebsd-fs@FreeBSD.org>, FreeBSD-scsi <freebsd-scsi@freebsd.org>, Steven Hartland <steven@multiplay.co.uk> Cc: Andriy Gapon <avg@FreeBSD.org> Subject: ZFS prefers iSCSI disks over local ones ? Message-ID: <9342D2A7-CE29-445B-9C40-7B6A9C960D59@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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Hi, I start a new thread to avoid confusion in the main one. (ZFS stalled after some mirror disks were lost) > On 03 Oct 2017, at 09:39, Steven Hartland wrote: >=20 >> On 03/10/2017 08:31, Ben RUBSON wrote: >>=20 >>> On 03 Oct 2017, at 09:25, Steven Hartland wrote: >>>=20 >>>> On 03/10/2017 07:12, Andriy Gapon wrote: >>>>=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. So here is the gstat -dp : 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 The 4 active drives are the iSCSI targets of the above quoted pool. A local disk : 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 A iSCSI disk : 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 Sounds like then the faulty thing is the rotationrate set to 0 ? Thx, Ben
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