[DRBD-user] drbd overhead

Lars Ellenberg lars.ellenberg at linbit.com
Tue May 4 16:15:23 CEST 2004

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, May 04, 2004 at 04:41:44PM +0300, dhz_bf at walla.co.il wrote:
> I have performed an experiment to get some idea about the overhead of
> drbd when its partner (the secondary node) is down.
> I am using version 0.6.12 of drbd.
> The drbd has been in CState of  WFConnection.
> I have performed a certain operation on the disk and it tool about 5.5
> minutes when drbd was loaded and "owned" the disk on which the
> operation was performed.  The operation involved tar and gzip.
> I then took drbd down and mounted the partitions drbd "owns" directly.
> I retried the operation and it took 4.5 minutes.
> There was an additional factor that the disk drbd "owns" contains the
> file system of a number of remote machines.  These machines were idle
> at the time of the experiment.
> I looked at the code and it seemed to me like the overhead of drbd
> when the secondary node is down (and CState < Connected) is pretty
> small.  Yet, the times I measured with this experiment show about 25%
> overhead of drbd.
> Do these results look like the ones you got in your experiments?
> Is this level of overhead reasonable?

not at all.
definetly a chaching issue in your "experimental setup".
drbd "overhead" in unconnected state is typically within the uncertainty
of the measurement.

	Lars Ellenberg

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