[Lustre-discuss] Slow performance on the first IOR / iozone (Lustre)

[Oleg Drokin]

Hello!

On Mar 22, 2008, at 2:55 PM, Anand Bisen wrote:
>
> I have been trying to understand why successive execution of iozone
> (also with dd and IOR) produces increasing performance from first run
> to third run. After the third run the performance is constant.

I believe what you are seeing is a direct result of bitmap blocks  
being not
read at mount time. So it takes some time to cache bitmaps (And other
data structures) into memory
(and it happens during writes which hinders performance).
Once bitmaps are all read, performance stabilizes.

Hopefully Alex or Andreas might comment further on this, or perhaps  
remember
a bug number, Cray filed one some time ago, I think.

Bye,
     Oleg