Re: Concurrent write access

[Wolfgang Mader <Wolfgang_Mader@brain-frog.de>]

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On Thursday 09 July 2015 22:06:09 Hugo Mills wrote:
> On Thu, Jul 09, 2015 at 11:34:40PM +0200, Wolfgang Mader wrote:
> > Hi,
> > 
> > I have a btrfs raid10 which is connected to a server hosting
> > multiple virtual machine. Does btrfs support connecting the same
> > subvolumes of the same raid to multiple virtual machines for
> > concurrent read and write? The situation would be the same as, say,
> > mounting user homes from the same nfs share on different machines.
> 
>    It'll depend on the protocol you use to make the subvolumes visible
> within the VMs.
> 
>    btrfs subvolumes aren't block devices, so that rules out most of
> the usual approaches. However, there are two methods I've used which I
> can confirm will work well: NFS and 9p.
> 
>    NFS will work as a root filesystem, and will work with any
> host/guest, as long as there's a network connection between the two.
> 9p is, at least in theory, faster (particularly with virtio), but
> won't let you boot with the 9p device as your root FS. You'll need
> virtualiser support if you want to run a virtio 9p -- I know qemu/kvm
> supports this; I don't know if anything else supports it.


Thanks for the overview. It it qmeu/kvm in fact, to this is an option. Right 
now, however, I connect the discs as virtual discs and not the file system, 
but only to one virtual machine.

Best,
Wolfgang

> 
>    You can probably use Samba/CIFS as well. It'll be slower than the
> virtualised 9p, and not be able to host a root filesystem. I haven't
> tried this one, because Samba and I get on like a house on fire(*).
> 
>    Hugo.
> 
> (*) Screaming, shouting, people running away, emergency services.

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