[DRBD-user] blocking I/O with drbd

Volker mail at blafoo.org
Thu Jan 5 12:06:14 CET 2012

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


Hi,

> Once the host is live again, i will report if that did the trick :-)

As promised, here comes the follow-up.

Unfortunately 8.3.12 does not do the trick. The described behaviour with
the load rising after using dd is still present.

But i had the chance to test the I/O-Performance while the whole
environment (9 Servers having the drbd-device mounted via nfs) was under
very little use. Doing the dd's at 5am in the morning showed almost no
problems with I/O-Performance. I was even able to write 400MB to the
drbd-device without any problems regarding io-wait.

Doing the same dd at 9am made the load go up to around 15.

I can conclude, that since the behaviour is the same wth 8.3.8-1 and
8.3.12, this is most likely not a drbd-bug. Having no problems under low
usage in contrast to having problems under heavier usage shows, that the
problem is the underlying I/O-Subsystem not being able handle the amount
of I/O-Requests generated by the whole environment.

Im not sure where to go from here. If we find a solution, i'll let you
know... :-)

- volker



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