[DRBD-user] Re: drbd is performing at 12 MB/sec on recent hardware

Lars Ellenberg lars.ellenberg at linbit.com
Thu Oct 16 15:14:58 CEST 2008

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


On Thu, Oct 16, 2008 at 10:19:20AM +0200, Bart Coninckx wrote:
> > fix your local io subsystem.
> > fix your local io subsystem driver.
> >
> > check
> >  local io subsystem,
> >  (battery backed) write cache enabled?
> 
> Yes, I did that yesterday, I got from 13 MB/Sec to 16 MB/Sec. Better, but 
> still not good.
> 
> >  raid resync/rebuild/re-whatever going on at the same time?
> 
> nope, RAID has been built and is steady.
> 
> >  does the driver honor BIO_RW_SYNC?
> 
> errr ... how can I check that? /proc/driver/cciss/cciss0 does not reveal 
> anything about that.
> 
> >  does the driver introduce additional latency
> >  because of ill-advised "optimizations"?
> 
> I use a stock SLES 10 SP1 cciss driver. I did understand that the I/O 
> scheduler is not the best one. Perhaps you are referring to that?
> 
> > if local io subsystem is ok,
> > but DRBD costs more than a few percent in throughput,
> > check your local io subsystem on the other node!
> 
> That node is identical to the other one.
> 
> > if that is ok as well, check network for throughput,
> > latency and packet loss/retransmits.
> 
> scp gives me about 70 MB/Sec, so my guess is that things are more likely 
> related to drbd and local io. 

scp does not know about fsync.

use the same benchmark against drbd and non-drbd partition on that cciss...

> > only if all of that seems ok too,
> > check drbd configuration.
> 
> > > > Of course, I am inclined to advise an upgrade to SP2, which might help
> > > > with a newer cciss driver ;-)
> >
> > a-ha.
> 
> since I use OES2 which is not supported on SP2, I'm somewhat reluctant on 
> installing the kernel from SP2. Novell support will most likely be gone when 
> I do this ... 

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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