[DRBD-user] MySQL performance breakdown during resync to secondary node

Felix Frank ff at mpexnet.de
Tue Mar 27 16:48:16 CEST 2012

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


On 03/27/2012 04:24 PM, Jakob Curdes wrote:
> Not sure which mail you mean, the one with the active-active setup? It
> seems to me that this is a different issue.
> In the case here I would suspect that drbd in some way manages to block
> the mysql tables - but how, with innodb and only reading at a rate way
> below the disk speed?
> We are now trying to reproduce this, but it requires setting up the
> complete database application to simulate the DB load. One point to note

this reminds me: Have you tried fiddling with the no-disk-barriers option?
I've heard a remark about how barriers in the I/O layer don't play well
with InnoDB, because it has its own barriers in place. But then, I don't
have a good understanding of how DRBD barriers work.

> is that it is not only the database access; we see high IOWaits during
> sync - even with very low sync speeds.

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