Re: parted/LVM for ET [Re: [Libvir] Storage manager initial requirements and thoughts

On Tue, Mar 20, 2007 at 12:06:39PM +0000, Mark McLoughlin wrote: I like the idea of storage pools too, but not the impl described in that thread :-) Creating a loop back mounted sparse file & running LVM on it is utterly disasterous for both performanceand & data integrity. It will also not be portable to any non-Linux systems which don't have LVM. It is really unneccessary too, since most host machines already have plenty of other ways for us to deal with storage - and importantly these are consistent with current manual approaches to managing storage so we have good compatability with non-libvirt managed storage. - There are a couple of different types of storage pool - An LVM volume group - Block devices - A directory on a filesystem - Each storage pool can have zero or more storage volumes allocated - LVM volume group has multiple logical volumes - Block device has multiple partitions - A directory has multiple files (maybe sparse) - Each storage pool has some measure of free space - LVM volume group has unallocated physical extents - Block device has unpartitioned sectors - A directory has free space from underlying filesystem - Every host has at least one storage pool with free space - ie a directory on a filesystem. Some hosts may also have free LVM space, or unpartitioned block devices but we can't assume their presence in general. This lets us manage all existing VMs which are either device (LVM/block) or file based (/var/lib/xen/images) with the new APIs, so gives a good back compatability story. The performance & reliability are good, since we're avoiding extra layers of loopback. There are only a handful of operations we need to track to get an initially useful API: - Enumerate storage pools - Enumerate volumes within a pool - Extract metadata about pools (free space, UUID?) - Extract metadata about volumes (logical size, physical allocation, UUID) - Create volume. - Delete volume That's pretty much it. I'd be inclined to implement regular file based pool in terms of /var/lib/xen/images (or /var/lib/libvirt/images?) as a first target. Its by far the easiest since it merely requires use of POSIX apis, and is also completely cross-platform portable (which LVM isn't). Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=|