[DRBD-user] degraded write performace

[Duane Cox]

> Try running it longer, like 10x as long. Also, just to test it, try
> making a single-disk software raid1 out of /dev/sdb and telling drbd to
> use /dev/mdwhatever as it's backing store. I've seen wacky performance
> differences depending on the "most close" block device underlying a
> given store. Easily demonstrated with raw device access with aoe (aoe
> will use 512b frames if you just dd to the device, whereas if you use md
> on top of the aoe device you'll get multiples of 512b frames).

Please help me see the light...

How does the advice above have anything to do with writing to /dev/sdb
(which is just a single 36G 15K U160 seagate) when clearly write performace
to /dev/sdb degrades with each additional passing of the bechmark command
and only when the drbd module is loaded and not even in a connnected state?

(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.


Thanks
Duane Cox