@Sage, thanks for the info :) @Mark: > If you want to do sequential I/O, you should do it buffered > (so that the writes can be aggregated) or with a 4M block size > (very efficient and avoiding object serialization). The original benchmark has been performed with 4M block size. And as you can see I still get more IOPS with rand than seq... I just tried with 4M without direct I/O, still the same. I can print fio results if it's needed. > We do direct writes for benchmarking, not because it is a reasonable > way to do I/O, but because it bypasses the buffer cache and enables > us to directly measure cluster I/O throughput (which is what we are > trying to optimize). Applications should usually do buffered I/O, > to get the (very significant) benefits of caching and write aggregation. I know why I use direct I/O. It's synthetic benchmarks, it's far away from a real life scenario and how common applications works. I just try to see the maximum I/O throughput that I can get from my RBD. All my applications use buffered I/O. @Alexandre: is it the same for you? or do you always get more IOPS with seq? Thanks to all of you.. On Mon, Nov 19, 2012 at 5:54 PM, Mark Kampe <mark.kampe@xxxxxxxxxxx> wrote: > Recall: > 1. RBD volumes are striped (4M wide) across RADOS objects > 2. distinct writes to a single RADOS object are serialized > > Your sequential 4K writes are direct, depth=256, so there are > (at all times) 256 writes queued to the same object. All of > your writes are waiting through a very long line, which is adding > horrendous latency. > > If you want to do sequential I/O, you should do it buffered > (so that the writes can be aggregated) or with a 4M block size > (very efficient and avoiding object serialization). > > We do direct writes for benchmarking, not because it is a reasonable > way to do I/O, but because it bypasses the buffer cache and enables > us to directly measure cluster I/O throughput (which is what we are > trying to optimize). Applications should usually do buffered I/O, > to get the (very significant) benefits of caching and write aggregation. > > >> That's correct for some of the benchmarks. However even with 4K for >> seq, I still get less IOPS. See below my last fio: >> >> # fio rbd-bench.fio >> seq-read: (g=0): rw=read, bs=4K-4K/4K-4K, ioengine=libaio, iodepth=256 >> rand-read: (g=1): rw=randread, bs=4K-4K/4K-4K, ioengine=libaio, >> iodepth=256 >> seq-write: (g=2): rw=write, bs=4K-4K/4K-4K, ioengine=libaio, iodepth=256 >> rand-write: (g=3): rw=randwrite, bs=4K-4K/4K-4K, ioengine=libaio, >> iodepth=256 >> fio 1.59 >> Starting 4 processes >> Jobs: 1 (f=1): [___w] [57.6% done] [0K/405K /s] [0 /99 iops] [eta >> 02m:59s] >> seq-read: (groupid=0, jobs=1): err= 0: pid=15096 >> read : io=801892KB, bw=13353KB/s, iops=3338 , runt= 60053msec >> slat (usec): min=8 , max=45921 , avg=296.69, stdev=1584.90 >> clat (msec): min=18 , max=133 , avg=76.37, stdev=16.63 >> lat (msec): min=18 , max=133 , avg=76.67, stdev=16.62 >> bw (KB/s) : min= 0, max=14406, per=31.89%, avg=4258.24, >> stdev=6239.06 >> cpu : usr=0.87%, sys=5.57%, ctx=165281, majf=0, minf=279 >> IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >> >=64=100.0% >> submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >=64=0.0% >> complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >=64=0.1% >> issued r/w/d: total=200473/0/0, short=0/0/0 >> >> lat (msec): 20=0.01%, 50=9.46%, 100=90.45%, 250=0.10% >> rand-read: (groupid=1, jobs=1): err= 0: pid=16846 >> read : io=6376.4MB, bw=108814KB/s, iops=27203 , runt= 60005msec >> slat (usec): min=8 , max=12723 , avg=33.54, stdev=59.87 >> clat (usec): min=4642 , max=55760 , avg=9374.10, stdev=970.40 >> lat (usec): min=4671 , max=55788 , avg=9408.00, stdev=971.21 >> bw (KB/s) : min=105496, max=109136, per=100.00%, avg=108815.48, >> stdev=648.62 >> cpu : usr=8.26%, sys=49.11%, ctx=1486259, majf=0, minf=278 >> IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >> >=64=100.0% >> submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >=64=0.0% >> complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >=64=0.1% >> issued r/w/d: total=1632349/0/0, short=0/0/0 >> >> lat (msec): 10=83.39%, 20=16.56%, 50=0.04%, 100=0.01% >> seq-write: (groupid=2, jobs=1): err= 0: pid=18653 >> write: io=44684KB, bw=753502 B/s, iops=183 , runt= 60725msec >> slat (usec): min=8 , max=1246.8K, avg=5402.76, stdev=40024.97 >> clat (msec): min=25 , max=4868 , avg=1384.22, stdev=470.19 >> lat (msec): min=25 , max=4868 , avg=1389.62, stdev=470.17 >> bw (KB/s) : min= 7, max= 2165, per=104.03%, avg=764.65, >> stdev=353.97 >> cpu : usr=0.05%, sys=0.35%, ctx=5478, majf=0, minf=21 >> IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.3%, >> >=64=99.4% >> submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >=64=0.0% >> complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >=64=0.1% >> issued r/w/d: total=0/11171/0, short=0/0/0 >> >> lat (msec): 50=0.21%, 100=0.44%, 250=0.97%, 500=1.49%, 750=4.60% >> lat (msec): 1000=12.73%, 2000=66.36%, >=2000=13.20% >> rand-write: (groupid=3, jobs=1): err= 0: pid=20446 >> write: io=208588KB, bw=3429.5KB/s, iops=857 , runt= 60822msec >> slat (usec): min=10 , max=1693.9K, avg=1148.15, stdev=15210.37 >> clat (msec): min=22 , max=5639 , avg=297.37, stdev=430.27 >> lat (msec): min=22 , max=5639 , avg=298.52, stdev=430.84 >> bw (KB/s) : min= 0, max= 7728, per=31.44%, avg=1078.21, >> stdev=2000.45 >> cpu : usr=0.34%, sys=1.61%, ctx=37183, majf=0, minf=19 >> IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >> >=64=99.9% >> submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >=64=0.0% >> complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >> >=64=0.1% >> issued r/w/d: total=0/52147/0, short=0/0/0 >> >> lat (msec): 50=2.82%, 100=25.63%, 250=46.12%, 500=10.36%, 750=5.10% >> lat (msec): 1000=2.91%, 2000=5.75%, >=2000=1.33% >> >> Run status group 0 (all jobs): >> READ: io=801892KB, aggrb=13353KB/s, minb=13673KB/s, maxb=13673KB/s, >> mint=60053msec, maxt=60053msec >> >> Run status group 1 (all jobs): >> READ: io=6376.4MB, aggrb=108814KB/s, minb=111425KB/s, >> maxb=111425KB/s, mint=60005msec, maxt=60005msec >> >> Run status group 2 (all jobs): >> WRITE: io=44684KB, aggrb=735KB/s, minb=753KB/s, maxb=753KB/s, >> mint=60725msec, maxt=60725msec >> >> Run status group 3 (all jobs): >> WRITE: io=208588KB, aggrb=3429KB/s, minb=3511KB/s, maxb=3511KB/s, >> mint=60822msec, maxt=60822msec >> >> Disk stats (read/write): >> rbd1: ios=1832984/63270, merge=0/0, ticks=16374236/17012132, >> in_queue=33434120, util=99.79% -- 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
