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



On Tue, Mar 20, 2007 at 02:58:16PM +0000, David Edmondson wrote:
> On Tue, Mar 20, 2007 at 02:32:10PM +0000, Daniel P. Berrange wrote:
> >  - 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.
> 
> ZFS takes a slightly different view:
> 
>     - ZFS storage pools are collections of physical devices (including
>       data replication),
>     - ZFS datasets are contained within ZFS storage pools and are
>       either filesystems, volumes or snapshots.
>     - ZFS filesystems are, well, filesystems,
>     - ZFS volumes are available as block devices,
>     - ZFS volumes can contain multiple partitions.

That all makes sense - the ZFS storage pools sounds like they provide
equivalent volume management capabilities to what you'd get in LVM.

> Currently we anticipate using both file-based images (inside ZFS and
> other filesystems) and ZFS volumes (to provide the impression of a
> dedicated physical device) for VMs, as well as dedicating real
> physical volumes, obviously.
> 
> Overall this fits with your model, I think.

Yes, sounds just fine. On this subject, does ZFS come with any library API
for doing all the volume pool management tasks, or is it all just a set
of command line tools as we'd get with LVM ?

Regards,
Dan.
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