[DRBD-user] Inconsistent performance

Peet de Vos peet at orax.co.za
Wed Mar 10 11:29:19 CET 2010

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

Hi everybody,

I have an OLTP application running on a 2 node cluster on top of DRBD.

( App: CentOS Linux --> MySql --> Perl --> Apache )
( Disk: Disk Partition --> LV --> DRBD --> Mount point )
( Cluster: DRBD <-- primary/primary --> DRBD )

Before I moved to this DRBD cluster setup, my response-time-graph was  
very consistent and stable (flatline).
After I moved to DRBD, the response-time-graph became inconsistent  
with peaks that don't make sense. Eg. typical response time would be  
0.2 seconds. Now I have responses of, for instance 3 or more seconds  
every now and then).  The cluster hardware have more CPU's, more  
memory, faster everything, and yet the response-times are slower and  
less consistent than my "no DRBD" setup.  It's been running in  
production with DRBD for several months.  Everything seems stable,  
other than the inconsistent performance.

Could this be a misconfiguration on my part (or lack of tuning), or is  
this normal?  The server load is under 40%.  The disks aren't very  
busy either.  The response-time-graph is fed by a few queries on the  
database across important tables.

Any guidance or help will be MUCHOS appreciated :)

Thanks and Regards,

Peet de Vos
Orax Solutions
082 629 9915
peet at orax.co.za
Fax: +27 12 803 5084 - P.O.Box 75250, Lynnwood Ridge, 0040, Pretoria,  
South Africa

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