[DRBD-user] Diagnosing DRBD Slowness

Peter Sabaini peter at sabaini.at
Tue Oct 21 23:53:15 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 Tuesday 21 October 2008 23:46:47 Lars Ellenberg wrote:
> 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 :)

Right, I did forget to redirect to /dev/null. Damn invisible null bytes!

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


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