Re: Concurrent write access

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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.

   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.

-- 
Hugo Mills             | Alert status mauve ocelot: Slight chance of
hugo@... carfax.org.uk | brimstone. Be prepared to make a nice cup of tea.
http://carfax.org.uk/  |
PGP: E2AB1DE4          |

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