[Lustre-discuss] O_DIRECT

[Andreas Dilger]

On 2010-08-14, at 1:32, Michael Kluge <Michael.Kluge at tu-dresden.de> wrote:
> how does Lustre handle write() requests to files opened with O_DIRECT. 
> Does the OSS enforce that the OST has physically written the data to the 
> OST before the op is completed or does the write() call return on the 
> client before this?

The write will be submitted directly from the client to the OST, and the OST always does synchronous writes, regardless of whether it is O_DIRECT or not. It cannot return from the syscall until the write is complete, because those pages are shared from userspace. 

Cheers, Andreas