Date: Tue, 3 Oct 2017 16:18:50 +0100 From: Gary Palmer <gpalmer@freebsd.org> To: Ben RUBSON <ben.rubson@gmail.com> Cc: Steven Hartland <steven@multiplay.co.uk>, FreeBSD-scsi <freebsd-scsi@freebsd.org>, Freebsd fs <freebsd-fs@FreeBSD.org>, Andriy Gapon <avg@FreeBSD.org> Subject: Re: ZFS prefers iSCSI disks over local ones ? Message-ID: <20171003151850.GA65538@in-addr.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>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, Oct 03, 2017 at 05:03:18PM +0200, Ben RUBSON wrote: > > On 03 Oct 2017, at 16:58, Steven Hartland <steven@multiplay.co.uk> wrote: > > > > 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 > > 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 ! Use the "option" setting in ctl.conf to change the rpm value (documented in the OPTIONS section of ctladm(8)). Regards, Gary
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20171003151850.GA65538>