2013/7/10 Gregory Farnum <greg@xxxxxxxxxxx>: > On Tue, Jul 9, 2013 at 7:08 PM, Li Wang <liwang@xxxxxxxxxxxxxxx> wrote: >> Hi, >> We did a simple throughput test on Ceph with 2 OSD nodes configured >> with one replica policy. For each OSD node, the throughput measured by 'dd' >> run locally is 117MB/s. Therefore, in theory, the two OSDs could provide >> 200+MB/s throughput. However, using 'iozone' from clients we only get a peak >> throughput at around 40MB/s. Is that because a write will incur 2 replica * >> 2 journal write? That is, writing into journal >> and replica doubled the traffic, respectively, which results in a total >> 4x write amplification. Is that true, or our understanding is wrong, >> and some performance tuning hint? > > Well, that write amplification is certainly happening. However, I'd > expect to get a better ratio out of the disk than that. Couple things > to check: > 1) is your benchmark dispatching multiple requests at a time, or just > one? (the latency on a single request is going to make throughput > numbers come out badly.) > 2) How do your disks handle two simultaneous write streams? (Most > disks should be fine, but sometimes they struggle.) > -Greg > Software Engineer #42 @ http://inktank.com | http://ceph.com > -- > 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 I have the same problem: 2 machines with several osds each, default replica count (2), btrfs on osd partitions, default journal location (file on a osd partition), journal size 2Gb, ceph 0.65, 1 Gbit network between machines that is shared with the client. dd benchmark shows ~ 110 Mb/s on osd partition. Object write via librados: 1 object - 43 Mb/s, 3 parallel objects - 66 Mb/s. At the same time I monitor osd partitions with iostat. Partitions are loaded 85-110 Mb/s. If I shutdown one node, write occurs only on one partition on one machine. Same results: disk is loaded 85-110 Mb/s and I get same throughput on client - 49 Mb/s for single obj and 66 Mb/s for 3 parallel objects. We are deciding whether to use ceph in production and we are stuck due to our weak understanding of this situation. -- 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
