[DRBD-user] Identifying High iowait on DRBD Computers

James Masson james.masson at lmax.com
Thu Feb 17 11:32:33 CET 2011

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

I'm interested in this too....

I'm not sure how reliable iowait is as a metric on DRBD volumes - I've had it return more than 90%
iowait on DRBD volumes doing a fraction of the iops that they're capable of at peak. Spindles on
both sides were barely at 50% iowait, network and cpu well within limits.

It would be nice to have a process to isolate where DRBD thinks the bottlenecks are, at the moment
it's a bit of a black box.

James M

On 17/02/11 06:41, Robinson, Eric wrote:
> While performing a resync, iostat shows that nodeA (primary) is doing almost all reads while nodeB
> (secondary) is doing almost all writes, which is expected. However, I'm trying to see the names
> of the processes that are doing the reading and writing. I tried enabling /proc/sys/vm/block_dump
> and checking dmesg, but most of what I see in there is kjournald. Do DRBD processes not show up in
> kernel debug output? If not, how do I isolate the source of constant 25-50% iowait on a computer
> running DRBD?
> --
> Eric Robinson
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