On Thu, May 23, 2013 at 11:01:47AM +0000, James Harper wrote:
You say "One is to use a single BTRFS filesystem with RAID-1 for all the storage and then have each VM use a file on that big BTRFS filesystem for all it's storage"
note that if you don't have any other particular reasons to use btrfs rather than zfs, then zfs is a better choice for this job. zfs allows you to create disk volumes (called "zvol") as well as filesystems from the pool, which are similar to a disk partition or an LVM logical volume but with better performance and all the other benefits of being part of a zpool. http://zfsonlinux.org/example-zvol.html http://pthree.org/2012/12/21/zfs-administration-part-xiv-zvols/ a zvol can also be exported via iscsi, so a VM on a compute node could use a zvol exported from a zfs file-server. could even use 2 or more zvols from different servers and raid them with mdadm (i haven't tried this myself but there's no reason why it shouldn't work - synchronised snapshotting may be problematic, you'd probably want to pause the VM briefly so you can snapshot the zvols on the file servers). btrfs doesn't yet have a zvol-like feature (i have no idea when or even if it is planned), so the only option there for a KVM or Xen VM is to use a large file as a qcow2 or whatever disk image. the btrfs wiki mentions "btrvols" on the Project Ideas page but it looks like no-one's even working on it yet. https://btrfs.wiki.kernel.org/index.php/Project_ideas#block_devices_.27btrvo... and, of course, with container-style VMs, you could use a btrfs subvolume or zfs filesystem. craig -- craig sanders <cas@taz.net.au>