[DRBD-user] MySQL-over-DRBD Performance

Lars Ellenberg lars.ellenberg at linbit.com
Tue Dec 18 19:41:01 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 Tue, Dec 18, 2007 at 07:13:05PM +0100, Lars Ellenberg wrote:
> please do
>   one-node# ping -w 10 -f -s 4100 replication-link-ip-of-other-node
> and show me the output.


 drbdadm disconnect you-resource-name
 drbd now StandAlone Primary/Unknown
 dd if=/dev/zero bs=4096 count=10000 of=/some/file/on/your/drbd oflag=dsync

 drbdadm adjust all
 wait for the resync
 drbd now Connected Primary/Secondary
 dd if=/dev/zero bs=4096 count=10000 of=/some/file/on/your/drbd oflag=dsync

 dd if=/dev/zero bs=4096 count=10000 of=/some/file/NOT/on/your/drbd oflag=dsync

do each dd command several times,
do this when nothing else happens on the box.

the important part here is the "dsync" flag.
if your dd does not know about that, upgrade.

the dd bs=4096 count=10000 oflag=sync
(many small requests, each single one of them synchronous by itself)
is to give an idea for the average latency of one single write request,
  * with drbd disconnected
  * with drbd connected 
  * without drbd (should be as close as possible to the lower level
    device of drbd, preferably on the same hardware)

the "ping -w 10 -f -s 4100" is to give an idea for the
average round-tripp time between your nodes.

together, it gives an expectation
of what should theoretically be possible to reach.

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