[DRBD-user] Huge max latency with sequential writes

Weilin Gong wgong at alcatel-lucent.com
Sat Jan 6 00:29:35 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.


Resend after re-formating the data table.

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   |0.0000  
>     |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 version is 0.7.11, 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
> _______________________________________________
> drbd-user mailing list
> drbd-user at lists.linbit.com
> http://lists.linbit.com/mailman/listinfo/drbd-user
>   

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