On Sat, Jan 12, 2013 at 2:57 PM, Chen, Xiaoxi <xiaoxi.chen@xxxxxxxxx> wrote: > > Hi list, > For a rbd write request, Ceph need to do 3 writes: > 2013-01-10 13:10:15.539967 7f52f516c700 10 filestore(/data/osd.21) _do_transaction on 0x327d790 > 2013-01-10 13:10:15.539979 7f52f516c700 15 filestore(/data/osd.21) write meta/516b801c/pglog_2.1a/0//-1 36015~147 > 2013-01-10 13:10:15.540016 7f52f516c700 15 filestore(/data/osd.21) path: /data/osd.21/current/meta/DIR_C/pglog\u2.1a__0_516B801C__none > 2013-01-10 13:10:15.540164 7f52f516c700 15 filestore(/data/osd.21) write meta/28d2f4a8/pginfo_2.1a/0//-1 0~496 > 2013-01-10 13:10:15.540189 7f52f516c700 15 filestore(/data/osd.21) path: /data/osd.21/current/meta/DIR_8/pginfo\u2.1a__0_28D2F4A8__none > 2013-01-10 13:10:15.540217 7f52f516c700 10 filestore(/data/osd.21) _do_transaction on 0x327d708 > 2013-01-10 13:10:15.540222 7f52f516c700 15 filestore(/data/osd.21) write 2.1a_head/8abf341a/rb.0.106e.6b8b4567.0000000002d3/head//2 3227648~524288 > 2013-01-10 13:10:15.540245 7f52f516c700 15 filestore(/data/osd.21) path: /data/osd.21/current/2.1a_head/rb.0.106e.6b8b4567.0000000002d3__head_8ABF341A__2 > > If using XFS as backend file system and running xfs on top of traditional sata disk, it will introduce a lot of seeks and therefore reduce bandwidth, a blktrace is available here :( http://ww3.sinaimg.cn/mw690/6e1aee47jw1e0qsbxbvddj.jpg) to demonstrate this issue.( single client running dd on top of a new RBD volumes). > Then I tried to move /osd.X/current/meta to a separate disk, the bandwidth boosted.(look blktrace at http://ww4.sinaimg.cn/mw690/6e1aee47jw1e0qsadz1bij.jpg). > I haven't test other access pattern or something else, but it looks to me that moving such meta to a separate disk (ssd or sata with btrfs) will benefit ceph write performance, is it true? Will ceph introduce this feature in the future? Is there any potential problem for such hack? > Did you try putting XFS metadata log a separate and fast device (mkfs.xfs -l logdev=/dev/sdbx,size=10000b). I think it will boost performance too. Regards Yan, Zheng -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
