Hello,
i have 2 OSD's and 3 MON's. Every OSD is on a 2,5TB LVM/EXT4 storage.
Why is the access to the rbd device so slow and what is meaning with
"Stddev Bandwidth" in rados bench? See the below statistics:
#Create a 1GB file on local Storage and test a local OSD for bandwidth
cd /ceph/; dd if=/dev/zero of=test.img bs=1GB count=1 oflag=direct
1+0 Datensätze ein
1+0 Datensätze aus
1000000000 Bytes (1,0 GB) kopiert, 1,8567 s, 539 MB/s
ceph tell osd.0 bench
{ "bytes_written": 1073741824,
"blocksize": 4194304,
"bytes_per_sec": "559979881.000000"}
#Create a pool and test the bandwidth
rados -p vmfs bench 30 write
Maintaining 16 concurrent writes of 4194304 bytes for up to 30 seconds
or 0 objects
Object prefix: benchmark_data_ceph-mh-3_9777
sec Cur ops started finished avg MB/s cur MB/s last lat avg lat
0 0 0 0 0 0 - 0
1 16 94 78 311.879 312 0.206434 0.182676
2 16 191 175 349.897 388 0.177737 0.175261
3 16 282 266 354.578 364 0.244247 0.173725
4 15 372 357 356.918 364 0.167184 0.175167
5 16 457 441 352.72 336 0.178794 0.177867
6 16 553 537 357.923 384 0.244694 0.175324
7 16 645 629 359.351 368 0.193504 0.175503
8 16 725 709 354.424 320 0.235158 0.177618
9 15 810 795 353.244 344 0.166452 0.179567
10 16 888 872 348.715 308 0.15287 0.181171
11 16 975 959 348.64 348 0.114494 0.181629
12 16 1066 1050 349.864 364 0.233927 0.181363
13 15 1136 1121 344.795 284 0.128635 0.184239
14 16 1231 1215 347.019 376 0.192001 0.182952
15 16 1313 1297 345.747 328 0.200144 0.183385
16 16 1334 1318 329.389 84 0.146472 0.183347
17 16 1416 1400 329.303 328 0.14064 0.193126
18 16 1500 1484 329.67 336 0.145509 0.193292
19 15 1594 1579 332.315 380 0.178459 0.191693
2013-12-26 17:15:24.083583min lat: 0.070546 max lat: 1.17479 avg lat:
0.191293
sec Cur ops started finished avg MB/s cur MB/s last lat avg lat
20 16 1665 1649 329.697 280 0.147855 0.191293
21 16 1701 1685 320.854 144 0.169078 0.198584
22 16 1750 1734 315.178 196 0.326568 0.201798
23 16 1805 1789 311.038 220 0.280829 0.203922
24 16 1882 1866 310.903 308 0.249915 0.204755
25 15 1966 1951 312.064 340 0.178078 0.204584
26 16 2030 2014 309.731 252 0.181972 0.205929
27 16 2085 2069 306.406 220 0.423718 0.207918
28 16 2179 2163 308.888 376 0.14442 0.206487
29 16 2252 2236 308.302 292 0.166282 0.206932
30 16 2325 2309 307.756 292 0.271987 0.207166
Total time run: 30.272445
Total writes made: 2325
Write size: 4194304
Bandwidth (MB/sec): 307.210
Stddev Bandwidth: 90.9029
Max bandwidth (MB/sec): 388
Min bandwidth (MB/sec): 0
Average Latency: 0.208258
Stddev Latency: 0.122409
Max latency: 1.17479
Min latency: 0.070546
#Test the bandwidth on a rbd device
rbd -p vmfs create test --size 1024
rbd -p vmfs map test
dd if=/dev/rbd1 of=test.img bs=1GB count=1 oflag=direct
1+0 Datensätze ein
1+0 Datensätze aus
1000000000 Bytes (1,0 GB) kopiert, 12,4647 s, 80,2 MB/s
Thanks, Markus
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