[DRBD-user] syncer speed

lucas.j lukasz.jurewicz at gmail.com
Mon Dec 24 21:47:36 CET 2012

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-----Original Message-----
From: Digimer <lists at alteeve.ca>
Sent: 24 grudnia 2012 7:00
To: Walter Robert Ditzler <ditwal001 at gmail.com>
Cc: 'drbd-user' <drbd-user at lists.linbit.com>
Subject: Re: [DRBD-user] syncer speed

On 12/24/2012 05:48 AM, Walter Robert Ditzler wrote:
> hi to all,
> is there anyone who has experience in speed allocation for a double 10gbit/s
> 10gbase bounded with bound type 3?
> i configured ...
> ***
> syncer {
>     al-extents            31;
>     rate                     450M;
> ***
> ... but get back a copy speed of a 800mb dummy file of 46m/s.
> any help appreciated :-)
> happy x-mas,
> walter.

First, confirm what speed your network can sustain on it's own. Use
'iperf' if you can, it's my go-to tool for network performance testing.
Next, break out one of the backing storage devices, put a normal FS on
it (like ext4) and use something like bonnie++ (and be sure to set a
test size that is 2x your RAM) to test the bare storage maximum
sustained throughput.

Once you know how fast they are on their own, take the slower of the two
and that is the theoretical maximum speed that DRBD will achieve.
Generally, I set the 'syncer { rate xxM; }' to ~30% of that speed. If
you set syncer to be too fast, your normal I/O will suffer as the
background syncing will consume all your available bandwidth. This is
why the sync rate is set low by default.

If you set the  'syncer { rate xxM; }' to a speed higher than is
actually possible, it could actually hurt performance and, possibly,
stall the sync entirely.

To be clear;

The syncer rate is *not* the day to day performance speed. Normal I/O,
like writing a file to the FS on the DRBD resource, will always go as
fast as is possible. The syncer rate *only* effects the speed at which
out-of-sync blocks are copied over when one of the nodes has been
off-line and blocks changed on the remaining peer,


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