[DRBD-user] Re: strange performance problems with drbd

Lars Ellenberg Lars.Ellenberg at linbit.com
Mon May 8 13:25:40 CEST 2006

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

/ 2006-05-08 08:27:56 +0000
\ Torsten Neumann:
> Francis I. Malolot <francis_m at ...> writes:
> > 
> > >>>When putting linux software raid5 on top it goes unusable slow
> > 
> > Raid 5 slow performance is normal especially write because
> > it must read overhead blocks in the stripe to recreate the parity block.
> > 
> > Please look where is  the bottleneck.
> disk write without drbd 40MB/sec
> disk write with drbd (recent kernel) ~ 3MB/sec (gigabit link)
> So how can I check why drbd slows things so terrible down? Yes there is a
> bottleneck. But without drbd all seems fine, with drbd not.

see what io scheduler is in use
on servers I prefer "deadline".
you can switch to "deadline" like this:
  for q in /sys/block/*/queue/scheduler ; do
	echo deadline > "$q"
or by specifying a boot-time commandline parameter.

if that did not help yet,
check wether increasing "max-buffers"
and/or decreasing "max-epoch-size" in drbd.conf does help.

: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
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