[DRBD-user] Sync rate is 300K/s!

Lars Ellenberg lars.ellenberg at linbit.com
Thu Mar 22 20:49:15 CET 2007

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


On Wed, Mar 21, 2007 at 04:43:58PM +0000, James Vanns wrote:
> I have a crossover cable between two machines sporting 1GigE NICs.
> With DRBD 8.0.0 I'm getting a sync rate of '376 (320) K/sec' as
> reported by /proc/drbd! What gives!? This isn't normal as I had a
> better rate with beta 6 (I think). I have not put a cap on the maximum
> rate in the configuration file. I have also tried pausing the sync,
> adding a cap of ~600M, then resuming the sync all to no avail.
> 
> Anyone else experience this?

if by "not put a cap" you mean you did just not specify
the "syncer rate", it defaults to ~250K/sec ...

against common believe it does _not_ help to specify a ridiculous high
rate, it does hurt. if you do not want "to cap", you should put it in
the area of what your hardware is capable to deliver.
so if you can reasonably expect from your hardware that it will deliver,
say, 70 MByte / sec sustained sequential write, and you do not want to
reserve anything of that for application usage, you should specify a
sync rate of about 70 to 80 M.
(rate 600M will probably hurt more than it helps).
(and don't forget to "drbdadm adjust")

there also are "advanced" tunables, especially
max-buffers and unplug-watermark may help.
tune carefully, just using maximum settings is not going to be optimal,
sometimes even smaller values increase overall performance.

if nothing helps, post your hardware (NICs, used driver(version)
and io subsystem (and driver/version, if applicable).  maybe someone
with the same hardware has seen and solved your problems before.

-- 
: Lars Ellenberg                            Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH      Fax +43-1-8178292-82 :
: Vivenotgasse 48, A-1120 Vienna/Europe    http://www.linbit.com :
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