On Mon, Aug 22, 2016 at 3:29 PM, Wido den Hollander <w...@42on.com> wrote: > >> Op 22 augustus 2016 om 21:22 schreef Nick Fisk <n...@fisk.me.uk>: >> >> >> > -----Original Message----- >> > From: Wido den Hollander [mailto:w...@42on.com] >> > Sent: 22 August 2016 18:22 >> > To: ceph-users <ceph-users@lists.ceph.com>; n...@fisk.me.uk >> > Subject: Re: [ceph-users] udev rule to set readahead on Ceph RBD's >> > >> > >> > > Op 22 augustus 2016 om 15:17 schreef Nick Fisk <n...@fisk.me.uk>: >> > > >> > > >> > > Hope it's useful to someone >> > > >> > > https://gist.github.com/fiskn/6c135ab218d35e8b53ec0148fca47bf6 >> > > >> > >> > Thanks for sharing. Might this be worth adding it to ceph-common? >> >> Maybe, Ilya kindly set the default for krbd to 4MB last year in the kernel, >> but maybe having this available would be handy if people ever want a >> different default. It could be set to 4MB as well, with a note somewhere to >> point people at its direction if they need to change it. >> > > I think it might be handy to have the udev file as redundancy. That way it > can easily be changed by users. The udev file is already present, they just > have to modify it. > >> > >> > And is 16MB something we should want by default or does this apply to your >> > situation better? >> >> It sort of applies to me. With a 4MB readahead you will probably struggle to >> get much more than around 50-80MB/s sequential reads, as the read ahead will >> only ever hit 1 object at a time. If you want to get nearer 200MB/s then you >> need to set either 16 or 32MB readahead. I need it to stream to LTO6 tape. >> Depending on what you are doing this may or may not be required. >> > > Ah, yes. I a kind of similar use-case I went for using 64MB objects > underneath a RBD device. We needed high sequential Write and Read performance > on those RBD devices since we were storing large files on there. > > Different approach, kind of similar result.
Question: what scheduler were you guys using to facilitate the readahead on the RBD client? Have you noticed any difference between different elevators and have you tried blk-mq/scsi-mq? Thank you. -- Alex Gorbachev Storcium > > Wido > >> > >> > Wido >> > >> > > >> > > _______________________________________________ >> > > 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 _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
