RE: Seperate metadata disk for OSD
Hi Sage, Thanks for your mail~ Would you have a timetable about when such improvement can be ready?It's critical for non-btrfs filesystem. I am thinking about introducing flashcache into my configuration to cache such meta write, since flashcache working under the filesystem, I suppose it will not break the assumption inside Ceph. I will try it on tomorrow and come back with you ~ Thanks again for the helps! Xiaoxi -Original Message- From: Sage Weil [mailto:s...@inktank.com] Sent: 2013年1月13日 0:57 To: Chen, Xiaoxi Cc: Mark Nelson; Yan, Zheng ; ceph-devel@vger.kernel.org Subject: RE: Seperate metadata disk for OSD On Sat, 12 Jan 2013, Chen, Xiaoxi wrote: Hi Zheng? I have put XFS log to a separate disk, indeed it provide some performance gain but not that significant. Ceph's metadata is somehow separate(it's some files reside in OSD's disk), therefore,it cannot be helped by neither XFS journal log nor OSD's journal.That's why I am trying to put ceph's metadata(/data/osd.x/meta folder ) to a separate SSD disk. To Nelson, I did the experiment with just 1 client, if using more clients, the gain will not be that much. It looks to me that a single write from client side become 3 writes to disk is somehow a big overhead for in-place-update filesystem such like XFS since it introduce more seeks.Out-of-place-update filesystem will not suffer a lot for such pattern,I didn?t find this problem when I using BTRFS as backend filesystem. But forBTRFS, fragmentation is another performance killer, for a single RBD volume, if you did a lot of random write on it, the sequential read performance will drop to 30% of a new RBD volume. This make BTRFS unusable in production. Separate Ceph meta seems quite easy to me ( I just mount a partition to /data/osd.X/meta), is it right ? is there any potential problem in it? Unfortunately, yes. The ceph journal and fs sync are carefully timed. The ceph-osd assumes that syncfs(2) on the $osd_data/current/commit_op_seq file will sync everything, but if meta/ is another fs that isnt true. At the every least, the code needs to be modified to sync that as well. That said, there is a lot of improvement that can be had here. The three things we write are: the pg log the pg info, spread across the pg dir xattr and that pginfo file the actual io The pg log could go in leveldb, which would translate those writes into a single sequential stream across the entire OSD. And the PG info separate between the xattr and the file is far from optimal: most of that data doesn't actually change on each write. What little does is very small, and could be moved into the xattr, avoiding touching the file (which means an inode + data block write) at all. We need to look a bit more closely to see how difficult that will really be to implement, but I think it is promising! sage Xiaoxi -Original Message- From: Mark Nelson [mailto:mark.nel...@inktank.com] Sent: 2013?1?12? 21:36 To: Yan, Zheng Cc: Chen, Xiaoxi; ceph-devel@vger.kernel.org Subject: Re: Seperate metadata disk for OSD Hi Xiaoxi and Zheng, We've played with both of these some internally, but not for a production deployment. Mostly just for diagnosing performance problems. It's been a while since I last played with this, but I hadn't seen a whole lot of performance improvements at the time. That may have been due to the hardware in use, or perhaps other parts of Ceph have improved to the point where this matters now! On a side note, Btrfs also had a google summer of code project to let you put metadata on an external device. Originally I think that was supposed to make it into 3.7, but am not sure if that happened. Mark On 01/12/2013 06:21 AM, Yan, Zheng wrote: On Sat, Jan 12, 2013 at 2:57 PM, Chen, Xiaoxi xiaoxi.c...@intel.com 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
RE: Seperate metadata disk for OSD
On Mon, 14 Jan 2013, Chen, Xiaoxi wrote: Hi Sage, Thanks for your mail~ Would you have a timetable about when such improvement can be ready?It's critical for non-btrfs filesystem. I am thinking about introducing flashcache into my configuration to cache such meta write, since flashcache working under the filesystem, I suppose it will not break the assumption inside Ceph. I will try it on tomorrow and come back with you ~ Thanks again for the helps! I think avoiding the pginfo change may be pretty simple. The log one I am a bit less concerned about (the appends from many rbd IOs will get aggregated into a small number of XFS IOs), and changing that around would be a bigger deal. sage Xiaoxi -Original Message- From: Sage Weil [mailto:s...@inktank.com] Sent: 2013?1?13? 0:57 To: Chen, Xiaoxi Cc: Mark Nelson; Yan, Zheng ; ceph-devel@vger.kernel.org Subject: RE: Seperate metadata disk for OSD On Sat, 12 Jan 2013, Chen, Xiaoxi wrote: Hi Zheng? I have put XFS log to a separate disk, indeed it provide some performance gain but not that significant. Ceph's metadata is somehow separate(it's some files reside in OSD's disk), therefore,it cannot be helped by neither XFS journal log nor OSD's journal.That's why I am trying to put ceph's metadata(/data/osd.x/meta folder ) to a separate SSD disk. To Nelson, I did the experiment with just 1 client, if using more clients, the gain will not be that much. It looks to me that a single write from client side become 3 writes to disk is somehow a big overhead for in-place-update filesystem such like XFS since it introduce more seeks.Out-of-place-update filesystem will not suffer a lot for such pattern,I didn?t find this problem when I using BTRFS as backend filesystem. But forBTRFS, fragmentation is another performance killer, for a single RBD volume, if you did a lot of random write on it, the sequential read performance will drop to 30% of a new RBD volume. This make BTRFS unusable in production. Separate Ceph meta seems quite easy to me ( I just mount a partition to /data/osd.X/meta), is it right ? is there any potential problem in it? Unfortunately, yes. The ceph journal and fs sync are carefully timed. The ceph-osd assumes that syncfs(2) on the $osd_data/current/commit_op_seq file will sync everything, but if meta/ is another fs that isnt true. At the every least, the code needs to be modified to sync that as well. That said, there is a lot of improvement that can be had here. The three things we write are: the pg log the pg info, spread across the pg dir xattr and that pginfo file the actual io The pg log could go in leveldb, which would translate those writes into a single sequential stream across the entire OSD. And the PG info separate between the xattr and the file is far from optimal: most of that data doesn't actually change on each write. What little does is very small, and could be moved into the xattr, avoiding touching the file (which means an inode + data block write) at all. We need to look a bit more closely to see how difficult that will really be to implement, but I think it is promising! sage Xiaoxi -Original Message- From: Mark Nelson [mailto:mark.nel...@inktank.com] Sent: 2013?1?12? 21:36 To: Yan, Zheng Cc: Chen, Xiaoxi; ceph-devel@vger.kernel.org Subject: Re: Seperate metadata disk for OSD Hi Xiaoxi and Zheng, We've played with both of these some internally, but not for a production deployment. Mostly just for diagnosing performance problems. It's been a while since I last played with this, but I hadn't seen a whole lot of performance improvements at the time. That may have been due to the hardware in use, or perhaps other parts of Ceph have improved to the point where this matters now! On a side note, Btrfs also had a google summer of code project to let you put metadata on an external device. Originally I think that was supposed to make it into 3.7, but am not sure if that happened. Mark On 01/12/2013 06:21 AM, Yan, Zheng wrote: On Sat, Jan 12, 2013 at 2:57 PM, Chen, Xiaoxi xiaoxi.c...@intel.com 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
Re: Seperate metadata disk for OSD
On Sat, Jan 12, 2013 at 2:57 PM, Chen, Xiaoxi xiaoxi.c...@intel.com 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.6b8b4567.02d3/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.6b8b4567.02d3__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=1b). 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Seperate metadata disk for OSD
Hi Xiaoxi and Zheng, We've played with both of these some internally, but not for a production deployment. Mostly just for diagnosing performance problems. It's been a while since I last played with this, but I hadn't seen a whole lot of performance improvements at the time. That may have been due to the hardware in use, or perhaps other parts of Ceph have improved to the point where this matters now! On a side note, Btrfs also had a google summer of code project to let you put metadata on an external device. Originally I think that was supposed to make it into 3.7, but am not sure if that happened. Mark On 01/12/2013 06:21 AM, Yan, Zheng wrote: On Sat, Jan 12, 2013 at 2:57 PM, Chen, Xiaoxi xiaoxi.c...@intel.com 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.6b8b4567.02d3/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.6b8b4567.02d3__head_8ABF341A__2 l 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=1b). 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line unsubscribe ceph-devel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: Seperate metadata disk for OSD
Hi Zheng， I have put XFS log to a separate disk, indeed it provide some performance gain but not that significant. Ceph's metadata is somehow separate(it's some files reside in OSD's disk), therefore,it cannot be helped by neither XFS journal log nor OSD's journal.That's why I am trying to put ceph's metadata(/data/osd.x/meta folder ) to a separate SSD disk. To Nelson, I did the experiment with just 1 client, if using more clients, the gain will not be that much. It looks to me that a single write from client side become 3 writes to disk is somehow a big overhead for in-place-update filesystem such like XFS since it introduce more seeks.Out-of-place-update filesystem will not suffer a lot for such pattern,I didn’t find this problem when I using BTRFS as backend filesystem. But forBTRFS, fragmentation is another performance killer, for a single RBD volume, if you did a lot of random write on it, the sequential read performance will drop to 30% of a new RBD volume. This make BTRFS unusable in production. Separate Ceph meta seems quite easy to me ( I just mount a partition to /data/osd.X/meta), is it right ? is there any potential problem in it? Xiaoxi -Original Message- From: Mark Nelson [mailto:mark.nel...@inktank.com] Sent: 2013年1月12日 21:36 To: Yan, Zheng Cc: Chen, Xiaoxi; ceph-devel@vger.kernel.org Subject: Re: Seperate metadata disk for OSD Hi Xiaoxi and Zheng, We've played with both of these some internally, but not for a production deployment. Mostly just for diagnosing performance problems. It's been a while since I last played with this, but I hadn't seen a whole lot of performance improvements at the time. That may have been due to the hardware in use, or perhaps other parts of Ceph have improved to the point where this matters now! On a side note, Btrfs also had a google summer of code project to let you put metadata on an external device. Originally I think that was supposed to make it into 3.7, but am not sure if that happened. Mark On 01/12/2013 06:21 AM, Yan, Zheng wrote: On Sat, Jan 12, 2013 at 2:57 PM, Chen, Xiaoxi xiaoxi.c...@intel.com 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.6b8b4567.02d3/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.6b8b4567.02d3__head_8 ABF341A__2 l 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=1b). 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
