Date: Tue, 3 Oct 2017 15:58:22 +0100 From: Steven Hartland <steven@multiplay.co.uk> To: Ben RUBSON <ben.rubson@gmail.com>, Freebsd fs <freebsd-fs@FreeBSD.org>, FreeBSD-scsi <freebsd-scsi@freebsd.org> Cc: Andriy Gapon <avg@FreeBSD.org> Subject: Re: ZFS prefers iSCSI disks over local ones ? Message-ID: <caa120ab-5b88-8602-45b6-1fbbea9ad194@multiplay.co.uk> In-Reply-To: <9342D2A7-CE29-445B-9C40-7B6A9C960D59@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>
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On 03/10/2017 15:40, Ben RUBSON wrote: > 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: >> >>> On 03/10/2017 08:31, Ben RUBSON wrote: >>> >>>> On 03 Oct 2017, at 09:25, Steven Hartland wrote: >>>> >>>>> On 03/10/2017 07:12, Andriy Gapon wrote: >>>>> >>>>>> On 02/10/2017 21:12, Ben RUBSON wrote: >>>>>> >>>>>> Hi, >>>>>> >>>>>> On a FreeBSD 11 server, the following online/healthy zpool : >>>>>> >>>>>> 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 >>>>>> >>>>>> 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 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). >> 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 ? > > Absolutely 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. Regards Steve
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