[DRBD-user] Diagnosing DRBD Slowness

Lars Ellenberg lars.ellenberg at linbit.com
Tue Oct 21 23:46:47 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 Tue, Oct 21, 2008 at 10:55:34PM +0200, Peter Sabaini wrote:
> On Tuesday 21 October 2008 22:44:46 Robinson, Eric wrote:
> > Ben Clewett said:
> > > # drbdadm adjust
> >
> > This is fantastic. It took 3 days to sync 12.5%, but now in the past 10
> > minutes since the change, it has jumped to 27%. I'm happy as can be.
> >
> > Thanks are definitely in order.

maybe you forgot the "adjust" last time you added the syncer rate to the
config file? default is, for hysterical reasons: 250 kB/s, which is
about what you had seen so far.

> > I'm still puzzled about the output of the dd command, though...
> >
> > [root at ha03 download]# dd if=/dev/zero bs=1M count=100 | nc 2.1.1.1 10000
> > 10+0 records in
> > 9+0 records out
> > 9437184 bytes (9.4 MB) copied, 27.7838 seconds, 340 kB/s
> >
> > The numbers look pretty much the same whether I connect from nc to nc on
> > different hosts or the same host.
> 
> Yup seems odd...
> FWIW I get around 3.3Mb/s when using nc on my box' external IP, 127.0.0.1, or 
> a Unix Socket.


there is the pipe and memcopy overhead.
but, are you sure you have the listening nc's output go to /dev/null?
if it goes to the terminal, it will be damn slow
even though you won't see all the NUL being written to it :)

	nc -l 10000 > /dev/null &
	dd if=/dev/zero bs=1M count=100 | nc 127.0.0.1 10000

should be MUCH faster.


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

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