Re: [Xen-users] Sharing file/folder

[Javier Guerra Giraldez <javier@xxxxxxxxxxx>]

On Mon, Feb 14, 2011 at 1:37 PM, lucianobarreto@xxxxxxxxx
<lucianobarreto@xxxxxxxxx> wrote:
> I need to share some files between VMs. This files will be used to transfer
> some information (read/write). But I need do it without any network resource
> (NFS or others). I've tried to do it sharing a partition just for test
> proposes, but i see that when i create a file on one VM another can't see it
> and there isnt any concurrence in this approach.
> Anyone can help me??

to share files, you need a shared filesystem.  there are two main
classes of these:

- network filesystems: NFS, Samba, 9p, etc.  these work really well;
you shouldn't reject them without good reason.

- clustered filesystems: GFS, OCFS2, CXFS, etc. they're designed for
SAN systems where several hosts access the same storage box.  in VM
case, if you create a single partition accessible from several VMs you
get exactly the same situation, (shared block device) and need the
same solution.

what definitely won't work is to use a 'normal' filesystem (ext3/4,
XFS, ReiserFS, FAT, HPFS, NTFS, etc) on a shared partition (just like
it won't work in a shared block device).  Since every filesystem
aggressively caches metadata to avoid rereading the disk for every
access, a VM won't be 'notified' if another one modifies a directory,
so it won't 'notice' any change.  and worse, since now the cached
metadata isn't consistent with the content of the disk, any write will
result in a heavily corrupted filesystem.

better go with NFS

-- 
Javier

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