It may be due to rbd cache effect..
Try the following..
Run your test with direct = 1 both the cases and rbd_cache = false (disable all other rbd cache option as well). This should give you similar result like krbd.
In direct =1 case, we saw ~10-20% degradation if we make rbd_cache = true.
But, direct = 0 case, it could be more as you are seeing..
I think there is a delta (or need to tune properly) if you want to use rbd cache.
Thanks & Regards
Somnath
From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Rafael Lopez
Sent: Thursday, September 10, 2015 8:24 PM
To: ceph-users@xxxxxxxxxxxxxx
Subject: bad perf for librbd vs krbd using FIO
Hi all,
I am seeing a big discrepancy between librbd and kRBD/ext4 performance using FIO with single RBD image. RBD images are coming from same RBD pool, same size and settings for both. The librbd results are quite bad by comparison, and in addition if I scale up the kRBD FIO job with more jobs/threads it increases up to 3-4x results below, but librbd doesn't seem to scale much at all. I figured that it should be close to the kRBD result for a single job/thread before parallelism comes into play though. RBD cache settings are all default.
I can see some obvious differences in FIO output, but not being well versed with FIO I'm not sure what to make of it or where to start diagnosing the discrepancy. Hunted around but haven't found anything useful, any suggestions/insights would be appreciated.
RBD cache settings:
[root@rcmktdc1r72-09-ac rafaell]# ceph --admin-daemon /var/run/ceph/ceph-osd.659.asok config show | grep rbd_cache
"rbd_cache": "true",
"rbd_cache_writethrough_until_flush": "true",
"rbd_cache_size": "33554432",
"rbd_cache_max_dirty": "25165824",
"rbd_cache_target_dirty": "16777216",
"rbd_cache_max_dirty_age": "1",
"rbd_cache_max_dirty_object": "0",
"rbd_cache_block_writes_upfront": "false",
[root@rcmktdc1r72-09-ac rafaell]#
This is the FIO job file for the kRBD job:
[root@rcprsdc1r72-01-ac rafaell]# cat ext4_test
; -- start job file --
[global]
rw=rw
size=100g
filename=/mnt/rbd/fio_test_file_ext4
rwmixread=0
rwmixwrite=100
percentage_random=0
bs=1024k
direct=0
iodepth=16
thread=1
numjobs=1
[job1]
; -- end job file --
[root@rcprsdc1r72-01-ac rafaell]#
This is the FIO job file for the librbd job:
[root@rcprsdc1r72-01-ac rafaell]# cat fio_rbd_test
; -- start job file --
[global]
rw=rw
size=100g
rwmixread=0
rwmixwrite=100
percentage_random=0
bs=1024k
direct=0
iodepth=16
thread=1
numjobs=1
ioengine=rbd
rbdname=nas1-rds-stg31
pool=rbd
[job1]
; -- end job file --
Here are the results:
[root@rcprsdc1r72-01-ac rafaell]# fio ext4_test
job1: (g=0): rw=rw, bs=1M-1M/1M-1M/1M-1M, ioengine=sync, iodepth=16
fio-2.2.8
Starting 1 thread
job1: Laying out IO file(s) (1 file(s) / 102400MB)
Jobs: 1 (f=1): [W(1)] [100.0% done] [0KB/321.7MB/0KB /s] [0/321/0 iops] [eta 00m:00s]
job1: (groupid=0, jobs=1): err= 0: pid=37981: Fri Sep 11 12:33:13 2015
write: io=102400MB, bw=399741KB/s, iops=390, runt=262314msec
clat (usec): min=411, max=574082, avg=2492.91, stdev=7316.96
lat (usec): min=418, max=574113, avg=2520.12, stdev=7318.53
clat percentiles (usec):
| 1.00th=[ 446], 5.00th=[ 458], 10.00th=[ 474], 20.00th=[ 510],
| 30.00th=[ 1064], 40.00th=[ 1096], 50.00th=[ 1160], 60.00th=[ 1320],
| 70.00th=[ 1592], 80.00th=[ 2448], 90.00th=[ 7712], 95.00th=[ 7904],
| 99.00th=[11072], 99.50th=[11712], 99.90th=[13120], 99.95th=[73216],
| 99.99th=[464896]
bw (KB /s): min= 264, max=2156544, per=100.00%, avg=412986.27, stdev=375092.66
lat (usec) : 500=18.68%, 750=7.43%, 1000=2.11%
lat (msec) : 2=48.89%, 4=4.35%, 10=16.79%, 20=1.67%, 50=0.03%
lat (msec) : 100=0.03%, 250=0.02%, 500=0.01%, 750=0.01%
cpu : usr=1.24%, sys=45.38%, ctx=19298, majf=0, minf=974
IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
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=0.0%
issued : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
latency : target=0, window=0, percentile=100.00%, depth=16
Run status group 0 (all jobs):
WRITE: io=102400MB, aggrb=399740KB/s, minb=399740KB/s, maxb=399740KB/s, mint=262314msec, maxt=262314msec
Disk stats (read/write):
rbd0: ios=0/150890, merge=0/49, ticks=0/36117700, in_queue=36145277, util=96.97%
[root@rcprsdc1r72-01-ac rafaell]#
[root@rcprsdc1r72-01-ac rafaell]# fio fio_rbd_test
job1: (g=0): rw=rw, bs=1M-1M/1M-1M/1M-1M, ioengine=rbd, iodepth=16
fio-2.2.8
Starting 1 thread
rbd engine: RBD version: 0.1.9
Jobs: 1 (f=1): [W(1)] [100.0% done] [0KB/65405KB/0KB /s] [0/63/0 iops] [eta 00m:00s]
job1: (groupid=0, jobs=1): err= 0: pid=43960: Fri Sep 11 12:54:25 2015
write: io=102400MB, bw=121882KB/s, iops=119, runt=860318msec
slat (usec): min=355, max=7300, avg=908.97, stdev=361.02
clat (msec): min=11, max=1468, avg=129.59, stdev=130.68
lat (msec): min=12, max=1468, avg=130.50, stdev=130.69
clat percentiles (msec):
| 1.00th=[ 21], 5.00th=[ 26], 10.00th=[ 29], 20.00th=[ 34],
| 30.00th=[ 37], 40.00th=[ 40], 50.00th=[ 44], 60.00th=[ 63],
| 70.00th=[ 233], 80.00th=[ 241], 90.00th=[ 269], 95.00th=[ 367],
| 99.00th=[ 553], 99.50th=[ 652], 99.90th=[ 832], 99.95th=[ 848],
| 99.99th=[ 1369]
bw (KB /s): min=20363, max=248543, per=100.00%, avg=124381.19, stdev=42313.29
lat (msec) : 20=0.95%, 50=55.27%, 100=5.55%, 250=24.83%, 500=12.28%
lat (msec) : 750=0.89%, 1000=0.21%, 2000=0.01%
cpu : usr=9.58%, sys=1.15%, ctx=23883, majf=0, minf=2751023
IO depths : 1=1.2%, 2=3.0%, 4=9.7%, 8=68.3%, 16=17.8%, 32=0.0%, >=64=0.0%
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=92.5%, 8=4.3%, 16=3.2%, 32=0.0%, 64=0.0%, >=64=0.0%
issued : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
latency : target=0, window=0, percentile=100.00%, depth=16
Run status group 0 (all jobs):
WRITE: io=102400MB, aggrb=121882KB/s, minb=121882KB/s, maxb=121882KB/s, mint=860318msec, maxt=860318msec
Disk stats (read/write):
dm-1: ios=0/2072, merge=0/0, ticks=0/233, in_queue=233, util=0.01%, aggrios=1/2249, aggrmerge=7/559, aggrticks=9/254, aggrin_queue=261, aggrutil=0.01%
sda: ios=1/2249, merge=7/559, ticks=9/254, in_queue=261, util=0.01%
[root@rcprsdc1r72-01-ac rafaell]#
Cheers,
Raf
--
Rafael Lopez
Data Storage Administrator
Servers & Storage (eSolutions)
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