Re: Poor Direct-IO Performance with Lustre-2.1.5

Drokin, Oleg
2013-06-23T01:03:21Z

Hello!

On Jun 22, 2013, at 7:50 PM, Chan Ching Yu, Patrick
wrote:
>         Record Size 1024 KB

This is your problem.
DirectIO is synchronous in nature so only as much data as you fit into a single
syscall will be in flight at any given moment.
In this case you only have 1 RPC in flight.
The key to adequately performing DirectIO is to have read/write syscalls with a
lot of data. 8*num_stripes is the very minimum, I would think.
Even then you likely won''t get cached read/write performance unless you
run a very underpowered client that gets choked on memory copies.

Bye,
    Oleg