Hello Adam, On Thu, 16 Jun 2016 23:40:26 -0500 Adam Tygart wrote: > According to Sage[1] Bluestore makes use of the pagecache. I don't > believe read-ahead is a filesystem tunable in Linux, it is set on the > block device itself, therefore read-ahead shouldn't be an issue. > Thank's for that link, that's very welcome news. So all that RAM is not going to waste, the equivalent to dir-entries and inodes I guess is in the RocksDB, so that being able to grow accordingly in RAM would be a good thing, too. As for read-ahead, take a peek at these: https://www.mail-archive.com/ceph-users@xxxxxxxxxxxxxx/msg27674.html http://www.spinics.net/lists/ceph-devel/msg30010.html The "We are more dependent on client-side readahead with bluestore since there is no underlying filesystem below the OSDs helping us out." bit is what was stuck in my head. Thanks again, Christian > I'm not familiar enough with Bluestore to comment on the rest. > > [1] http://www.spinics.net/lists/ceph-devel/msg29398.html > > -- > Adam > > On Thu, Jun 16, 2016 at 11:09 PM, Christian Balzer <chibi@xxxxxxx> wrote: > > > > Hello, > > > > I don't have anything running Jewel yet, so this is for devs and people > > who have played with bluestore or read the code. > > > > With filestore, Ceph benefits from ample RAM, both in terms of > > pagecache for reads of hot objects and SLAB to keep all the > > dir-entries and inodes in memory. > > > > With bluestore not being a FS, I'm wondering what can and will be done > > for it to maximize performance by using available RAM. > > I doubt there's a dynamic cache allocation ala pagecache present or on > > the road-map. > > But how about parameters to grow caches (are there any?) and give the > > DB more breathing space? > > > > I suppose this also cuts into the current inability to do read-ahead > > with bluestore by itself (not client driven). > > > > The underlying reason for this of course to future proof OSD storage > > servers, any journal SSDs will be beneficial for RocksDB and WAL as > > well, but if available memory can't be utilized beyond what the OSDs > > need themselves it makes little sense to put extra RAM into them. > > > > Christian > > -- > > Christian Balzer Network/Systems Engineer > > chibi@xxxxxxx Global OnLine Japan/Rakuten Communications > > http://www.gol.com/ > > _______________________________________________ > > ceph-users mailing list > > ceph-users@xxxxxxxxxxxxxx > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- Christian Balzer Network/Systems Engineer chibi@xxxxxxx Global OnLine Japan/Rakuten Communications http://www.gol.com/ _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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