Re: [Xen-users] Sharing file/folder

[Melody Bliss <melodybliss@xxxxxxxxx>]

Another option is to use something like unison, which is a file synchronizer.

http://www.cis.upenn.edu/~bcpierce/unison/

You'd have independent filesystems, but have unison synchronize
(bi/multidirectionally) the files there. It works similarly to rsync
but changes can happen in either direction and it allows for N-way
synchronization.

The only problem being that you could theoretically modify a file in
multiple places. Unison will detect this and not perform an update
with user intervention.

Mel

On Mon, Feb 14, 2011 at 12:41 PM, lucianobarreto@xxxxxxxxx
<lucianobarreto@xxxxxxxxx> wrote:
> Sorry if duplicated...
> Thanks guys, let me expose my problem. I'm prototyping a fault tolerance
> server (byzantine fault tolerance). Vms need do comunicate each order for
> make decisions about requests. My host will be out of network (cant access
> anything) and my Vms can comunicate to the external world, but the decision
> need to be local. Yes, I could comunicate via network inside VM to exchange
> information but my propose is to have a reliable local share to do it. In
> another work a friend used a Virtualbox folder share to do it, but now I
> need increase performance and use Xen to do it.
> About clustered filesystems, any options to use it in a normal block device
> like Sata HD or SCSI? I understand..."clustered"... but any option?
> Thanks and I will get more information about clustered filesystems
> 2011/2/14 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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>> Xen-users@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-users
>
>
>
> --
> Luciano Barreto
>
> _______________________________________________
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> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
>



-- 
Melody Bliss
Usenix, SAGE and LOPSA Charter Member
Patron Member of the NRA

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