Nope, I`m using KVM for rbd guests. Surely I`ve been noticed that Sage mentioned too small value and I`ve changed it to 64M before posting previous message with no success - both 8M and this value cause a performance drop. When I tried to wrote small amount of data that can be compared to writeback cache size(both on raw device and ext3 with sync option), following results were made: dd if=/dev/zero of=/var/img.1 bs=10M count=10 oflag=direct (almost same without oflag there and in the following samples) 10+0 records in 10+0 records out 104857600 bytes (105 MB) copied, 0.864404 s, 121 MB/s dd if=/dev/zero of=/var/img.1 bs=10M count=20 oflag=direct 20+0 records in 20+0 records out 209715200 bytes (210 MB) copied, 6.67271 s, 31.4 MB/s dd if=/dev/zero of=/var/img.1 bs=10M count=30 oflag=direct 30+0 records in 30+0 records out 314572800 bytes (315 MB) copied, 12.4806 s, 25.2 MB/s
and so on. Reference test with bs=1M and count=2000 has slightly worse results _with_ writeback cache than without, as I`ve mentioned before. Here the bench results, they`re almost equal on both nodes: bench: wrote 1024 MB in blocks of 4096 KB in 9.037468 sec at 113 MB/sec Also, because I`ve not mentioned it before, network performance is enough to hold fair gigabit connectivity with MTU 1500. Seems that it is not interrupt problem or something like it - even if ceph-osd, ethernet card queues and kvm instance pinned to different sets of cores, nothing changes. On Mon, Mar 19, 2012 at 8:59 PM, Greg Farnum <gregory.far...@dreamhost.com> wrote: > It sounds like maybe you're using Xen? The "rbd writeback window" option only > works for userspace rbd implementations (eg, KVM). > If you are using KVM, you probably want 81920000 (~80MB) rather than 8192000 > (~8MB). > > What options are you running dd with? If you run a rados bench from both > machines, what do the results look like? > Also, can you do the ceph osd bench on each of your OSDs, please? > (http://ceph.newdream.net/wiki/Troubleshooting#OSD_performance) > -Greg > > > On Monday, March 19, 2012 at 6:46 AM, Andrey Korolyov wrote: > >> More strangely, writing speed drops down by fifteen percent when this >> option was set in vm` config(instead of result from >> http://www.mail-archive.com/ceph-devel@vger.kernel.org/msg03685.html). >> As I mentioned, I`m using 0.43, but due to crashed osds, ceph has been >> recompiled with e43546dee9246773ffd6877b4f9495f1ec61cd55 and >> 1468d95101adfad44247016a1399aab6b86708d2 - both cases caused crashes >> under heavy load. >> >> On Sun, Mar 18, 2012 at 10:22 PM, Sage Weil <s...@newdream.net >> (mailto:s...@newdream.net)> wrote: >> > On Sat, 17 Mar 2012, Andrey Korolyov wrote: >> > > Hi, >> > > >> > > I`ve did some performance tests at the following configuration: >> > > >> > > mon0, osd0 and mon1, osd1 - two twelve-core r410 with 32G ram, mon2 - >> > > dom0 with three dedicated cores and 1.5G, mostly idle. First three >> > > disks on each r410 arranged into raid0 and holds osd data when fourth >> > > holds os and osd` journal partition, all ceph-related stuff mounted on >> > > the ext4 without barriers. >> > > >> > > Firstly, I`ve noticed about a difference of benchmark performance and >> > > write speed through rbd from small kvm instance running on one of >> > > first two machines - when bench gave me about 110Mb/s, writing zeros >> > > to raw block device inside vm with dd was at top speed about 45 mb/s, >> > > for vm`fs (ext4 with default options) performance drops to ~23Mb/s. >> > > Things get worse, when I`ve started second vm at second host and tried >> > > to continue same dd tests simultaneously - performance fairly divided >> > > by half for each instance :). Enabling jumbo frames, playing with cpu >> > > affinity for ceph and vm instances and trying different TCP congestion >> > > protocols gave no effect at all - with DCTCP I have slightly smoother >> > > network load graph and that`s all. >> > > >> > > Can ml please suggest anything to try to improve performance? >> > >> > Can you try setting >> > >> > rbd writeback window = 8192000 >> > >> > or similar, and see what kind of effect that has? I suspect it'll speed >> > up dd; I'm less sure about ext3. >> > >> > Thanks! >> > sage >> > >> > >> > > >> > > ceph-0.43, libvirt-0.9.8, qemu-1.0.0, kernel 3.2 >> > > -- >> > > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in >> > > the body of a message to majord...@vger.kernel.org >> > > (mailto: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 >> (mailto: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
