[DRBD-user] degraded write performace

Duane Cox duanec at mail.illicom.net
Thu Mar 29 20:09:46 CEST 2007

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


> OK, I haven't been paying attention which means this is probably a
> stupid question, but is there a reason you're using the raw device
> instead of the drbd device when drbd is loaded?

Is it bad to test write performace to the raw device when drbd is loaded?
at this point I have no valid data, so I don't care about anything
destructive...

I was trying to determine where/when/how the problem (bottleneck) is
happening.
I have tried various tests, reading archived posts, and this kinda stuck out
as something peculiar and suspecious.

(drbd loaded in disconnected state)
initially I get ~70 MB/s write througput to /dev/sdb
eventually I get ~30 MB/s write througput to /dev/sdb
possible even gets worse, I just stopped testing at this point.
Then I STOP/UNLOAD drbd
now I get ~70 MB/s write throughpout to /dev/sdb again.


>...and does the drbd device show the same degradation?

Yes and no, meaning it's not the same... it starts out at a lower MB/s and
gets even worse.





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