I don't see it as being any worse than having multiple journals on a single drive. If your journal drive tanks, you're out X OSDs as well. It's arguably better, since the number of affected OSDs per drive failure is lower. Admittedly, neither deployment is ideal, but it an effective way to get from A to B for those of us with limited hardware options.
QH On Wed, Jul 8, 2015 at 10:32 AM, Mark Nelson <mnel...@redhat.com> wrote: > The biggest thing to be careful of with this kind of deployment is that > now a single drive failure will take out 2 OSDs instead of 1 which means > OSD failure rates and associated recovery traffic go up. I'm not sure > that's worth the trade-off... > > Mark > > On 07/08/2015 11:01 AM, Quentin Hartman wrote: > >> Regarding using spinning disks for journals, before I was able to put >> SSDs in my deployment I came up wit ha somewhat novel journal setup that >> gave my cluster way more life than having all the journals on a single >> disk, or having the journal on the disk with the OSD. I called it >> "interleaved journals". Essentially offset the journal location by one >> disk, so in a 4 disk system: >> >> OS disk sda has journal for sdb OSD >> sdb OSD disk has journal for sdc OSD >> sdc OSD disk has journal for sdd OSD >> sdd OSD disk has no journal on it >> >> This limited the contention substantially. When the cluster got busy >> enough that multiple OSDs on the same machine were writing >> simultaneously it still took a hit, but it was a big upgrade from the >> out of the box deployment. I also tried leaving the OS drive out and >> only interleaving the journals on the OSD drives, but that was slightly >> worse under load than this configuration. It seems that the contention >> of the journals and OSDs was stronger than the contention with logging. >> >> QH >> >> On Fri, Jul 3, 2015 at 1:23 AM, Van Leeuwen, Robert >> <rovanleeu...@ebay.com <mailto:rovanleeu...@ebay.com>> wrote: >> >> > Another issue is performance : you'll get 4x more IOPS with 4 x 2TB >> drives than with one single 8TB. >> > So if you have a performance target your money might be better >> spent on smaller drives >> >> Regardless of the discussion if it is smart to have very large >> spinners: >> Be aware that some of the bigger drives use SMR technology. >> Quoting wikipedia on SMR: >> "shingled recording writes new tracks that overlap part of the >> previously written magnetic track, leaving the previous track >> thinner and allowing for higher track density.” >> and >> "The overlapping-tracks architecture may slow down the writing >> process since writing to one track overwrites adjacent tracks, and >> requires them to be rewritten as well." >> >> Usually these these disks are marketed "for archival use". >> Generally speaking you really should not use these unless you >> exactly know which write workload is hitting the disk and it is just >> very big sequential writes. >> >> Cheers, >> Robert van Leeuwen >> >> _______________________________________________ >> ceph-users mailing list >> ceph-users@lists.ceph.com <mailto:ceph-users@lists.ceph.com> >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> >> >> >> >> _______________________________________________ >> ceph-users mailing list >> ceph-users@lists.ceph.com >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> >> _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >
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