[DRBD-user] Re: Huge max latency

Weilin Gong wgong at alcatel-lucent.com
Fri Jan 5 22:48:15 CET 2007

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


Forgot to mention, DRBD version is 0.7.11.

Weilin Gong wrote:
> Hi,
>
> I ran some drbd performance tests with 'tiobench':
>
> tiobench.pl --identifier drbd-connected --size 5000 --numruns 1 --dir 
> /secroot --block 4096 --threads 4
>
> noticed the huge max latency numbers with Sequential Writes:
>
> Unit information
> ================
> File size            = megabytes
> Blk Size            = bytes
> Rate                 = megabytes per second
> CPU%             = percentage of CPU used during the test
> Latency            = milliseconds
> Lat%                = percent of requests that took longer than X seconds
> CPU Eff           = Rate divided by CPU% - throughput per cpu load
>
> Identifier
>
> 	
>
> File Size
>
> 	
>
> Blk Size
>
> 	
>
> Num Thr
>
> 	
>
> Rate
>
> 	
>
> Maximum CPU%
>
> 	
>
> Avg Latency
>
> 	
>
> Max Latency
>
> 	
>
> Lat% >2s
>
> 	
>
> Lat% >10s
>
> 	
>
> CPU Eff
>
> Raw-device
>
> 	
>
> 5000
>
> 	
>
> 4096
>
> 	
>
> 4
>
> 	
>
> 31.24
>
> 	
>
> 26.80%
>
> 	
>
> 0.364
>
> 	
>
> 5635.06
>
> 	
>
> 0.00242
>
> 	
>
> 0.00000
>
> 	
>
> 117
>
> Drbd-disconnected
>
> 	
>
> 5000
>
> 	
>
> 4096
>
> 	
>
> 4
>
> 	
>
> 33.18
>
> 	
>
> 26.29%
>
> 	
>
> 0.319
>
> 	
>
> 110394.58
>
> 	
>
> 0.00190
>
> 	
>
> 0.00016
>
> 	
>
> 126
>
> Drbd-connected
>
> 	
>
> 5000
>
> 	
>
> 4096
>
> 	
>
> 4
>
> 	
>
> 20.88
>
> 	
>
> 50.18%
>
> 	
>
> 0.457
>
> 	
>
> 135712.09
>
> 	
>
> 0.00110
>
> 	
>
> 0.00008
>
> 	
>
> 42
>
>
> My lab setting:
>
>     * Two Linux nodes on 2.6.10_mvlcge401-pc_target-x86_pentium3-P3SMP.
>     * Dual-core Intel Xeon 2GHz CPU, 4GB Memory, 1Gbits/s network
>       interface.
>     * 5.7GB partition on SCSI disk, ext2 file system with the "-T
>       largefile4" option.
>     * DRBD rate=100M;  protocal C; sndbuf-size 1024k.
>
> I don't believe the disk (~50MB/s) or network may be the factors here. 
> You can see the big number jump even with the DRBD disconnected mode.
>
> Any help on analyzing/identifying the problem will be greatly appreciated.
>
> Weilin
>

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