[Gluster-devel] Using GlusterFs for virtual block devices.

Neil Wilson neil at brightbox.co.uk
Mon Jul 14 11:40:15 UTC 2008

I'm looking at using GlusterFS as the underlying clustered filesystem
for a set of (KVM based) virtual machines

My initial thoughts were to get the Host server to client-side mirror
between two GlusterFS bricks (one of which would probably be local),
create the virtual machine's boot disk as a file on the GlusterFS
filesystem and then provide that to the virtual machine as a loopback
block device.

A few questions spring to mind:

- Would the replication work as we expect, ie blocks are written to
two locations?
- Can you loopback mount files as block devices within virtual
machines on GlusterFs?
- How would the file resynchronise if one half of the mirror went
offline for a period of time? My understanding is that Gluster resyncs
when a file is opened. Obviously with a virtual disk drive the file is
only going to be opened and closed when the virtual machine reboots.

If anybody has any experience of issues with running virtual machines
over GlusterFS I'd love to hear from them.

Neil Wilson

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