Eric Schrock wrote:
On Tue, Aug 01, 2006 at 01:10:44PM +0200, Patrick Petit wrote:
Hi There,
I looked at the ZFS admin guide in attempt to find a way to leverage ZFS
capabilities (storage pool, mirroring, dynamic stripping, etc.) for Xen
domU file systems that are not ZFS. Couldn't find an answer whether ZFS
could be used only as a "regular" volume manager to create logical
volumes for UFS or even a Linux ext2fs, with ideally, the ability to
create snapshots and clones...
You can create a zvol, which is a ZFS pseudo-device:
That's great ! Is this documented in the admin guide? I haven't seen it.
# zfs create -V 50G pool/myvol
This will create a 50G volume at '/dev/zvol/dsk/pool/myvol'. You can
take advantage of standard ZFS features, including compression,
snapshots, clones, etc. Of course be careful snapshotting live volumes,
you may catch the filesystem in an inconsistent state and end up unhappy
if you rollback, clone, etc.
Sure, I understand that.
Also, what can we expect, performance wise, from a file-backed logical
block device created on ZFS? Generally, performance is bad due to the
beneath file system overhead in comparison to a physical block device.
Would ZFS perform good enough in this configuration?
Do you mean a pool created from files, or a zvol as described above?
I meant the former.
Creating pools from files is definitely not a good idea if you careabout
performance. You'll be going through two layers of filesystems,with all the
added overhead of the standard POSIX interface. If you mean the latter, you
should get good performance, though it will depend
on your workload. The volume talks directly to the DMU (data management
unit), bypassing the POSIX layer. You can even tune the volume block
size (with -b) to your workload - large streaming reads/writes can
benefit from a larger blocksize, depending on whether the filesystem
above can really take advantage of it.
Hope that helps,
Yes it does completely. Thank you.
- Patrick
- Eric
--
Eric Schrock, Solaris Kernel Development http://blogs.sun.com/eschrock
--
Patrick Petit Sun Microsystems Inc.
Labs, CTO - G2 Systems Exp. ICNC Grenoble (http://icncweb.france)
Phone: (+33)476 188 232 x38232 180, Avenue de l'Europe
Fax: (+33)476 188 282 38334 Saint-Ismier Cedex, France
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