AnsweredAssumed Answered

investigating RWSpeedTest results

Question asked by dimamah on Jan 1, 2014
Latest reply on Jan 9, 2014 by aaron

Hi, 
I ran the test on my cluster and got suspicious results.

 

 [root@cluster hadoop-0.20.2]# for i in `seq 5`; do bin/hadoop jar lib/maprfs-diagnostic-tools-1.0.3-mapr-3.0.1.jar com.mapr.fs.RWSpeedTest /t/y${i} 10000 maprfs:///; done;
    Write rate: 751.9908204245553 M/s
    Write rate: 818.0496177250741 M/s
    Write rate: 788.7588385737927 M/s
    Write rate: 797.5174931548524 M/s
    Write rate: 756.3300634737449 M/s
    
    [root@cluster hadoop-0.20.2]# for i in `seq 5`; do bin/hadoop jar lib/maprfs-diagnostic-tools-1.0.3-mapr-3.0.1.jar com.mapr.fs.RWSpeedTest /t/y${i} -10000 maprfs:///; done;
    Read rate: 183.70931006692598 M/s
    Read rate: 179.8339850449338 M/s
    Read rate: 171.02575394301186 M/s
    Read rate: 185.99357894176705 M/s
    Read rate: 179.8339850449338 M/s

 

While running dd (`dd if=/dev/sd$i bs=4M count=1000 of=/dev/null`) from all the disks simultaneously results in :

 

    4194304000 bytes (4.2 GB) copied, 23.9953 s, 175 MB/s
    4194304000 bytes (4.2 GB) copied, 21.8476 s, 192 MB/s
    4194304000 bytes (4.2 GB) copied, 22.2197 s, 189 MB/s
    4194304000 bytes (4.2 GB) copied, 22.6475 s, 185 MB/s
    4194304000 bytes (4.2 GB) copied, 23.028 s, 182 MB/s
    4194304000 bytes (4.2 GB) copied, 23.1582 s, 181 MB/s
    4194304000 bytes (4.2 GB) copied, 23.6283 s, 178 MB/s
    4194304000 bytes (4.2 GB) copied, 23.8413 s, 176 MB/s
    4194304000 bytes (4.2 GB) copied, 23.9408 s, 175 MB/s
    4194304000 bytes (4.2 GB) copied, 24.3096 s, 173 MB/s

 

Can you please elaborate on what the RWSpeedTest does exactly? 
Does it do IO on 1 disk only? 
Also, how is it that the Writes are much faster than the reads? Is it writing to the controller's cache only? 

 

The configuration is :

  • Controller : PERC H700 Integrated Firmware 12.10.1-0001
  • 10 Sata3 6gb disks
  • No raid.


Thanks, 
Dima.

Outcomes