Re: [Qemu-devel] migration question: disk images on nfs server

[Marcin Gibuła]

> It is more a NFS issue, if you have a file in NFS that two users in
> two different host are accessing (one at least write to it) you will
> need to enforce the "sync" option.
> Even if you flush all the data and close the file the NFS client can still
> have cached data that it didn't sync to the server.

Do you know if is applies to linux O_DIRECT writes as well?

From comment in fs/nfs/direct.c:

* When an application requests uncached I/O, all read and write requests
* are made directly to the server; data stored or fetched via these
* requests is not cached in the Linux page cache.  The client does not
* correct unaligned requests from applications.  All requested bytes are
* held on permanent storage before a direct write system call returns to
* an application.



--
mg