User-mode Linux kernel port

On Fri, Feb 01, 2002 at 08:43:24PM +1030, Richard Russell wrote:
> Hi all...

I think what you want is a covered by LVM snapshots:

http://www.sistina.com/lvm_howtos/lvm_howto/Taking_a_backup_using_sna.html

The scenario you mention isn't quite the same as that in the HOWTO but you can
use it in a similar way by making a snapshot of the /home filesystem each
evening and mounting that as a backup.

Patrick

> I think what you want is a covered by LVM snapshots:
> 
>
http://www.sistina.com/lvm_howtos/lvm_howto/Taking_a_backup_using_sna.ht
ml
> 
> The scenario you mention isn't quite the same as that in the HOWTO but
> you can use it in a similar way by making a snapshot of the /home
> filesystem each evening and mounting that as a backup.

Nice. I was completely unaware of the snapshot facility of LVM (and
indeed, unaware that LVM was usable on Linux)...

Thanks... How would this kind of thing compare against a generic COW
driver, for things like performance, stability, and likelyhood of being
usable shortly?

rr

-- 
Richard Russell
Yellow Goanna Pty Ltd
e: richard@...
m: +61 412 827 805
f: +61 8 8462 2362

On Fri, 1 Feb 2002, Richard Russell wrote:

> Hi all...
> 
> I'm new here, and was drawn here by an idea that I had that is closely
> related to UML... All I want is something equivalent to the ubd layered
> block device driver, in a standard kernel. I don't (at this stage) want
> to run full UML -- I just want to be able to use something like ubd for
> backups of my data directories...
> 
> My idea can be explained thusly:
> 
> Have a ubd master fs, which is a copy of your real /home fs -- make one
> of these per week...
> On a daily basis, make child ubd cow fs's (sorry, not familiar with the
> terminology) as incremental backups -- perhaps use rsync to copy from
> the real /home to the new child cow (calf?).
> 
> Mount these read only under /backup/<date>, and as far as users are
> concerned, they have an online copy of every day's work available in an

	http://www.stearns.org/rsync-backup/
	Daily snapshots, automatic hardlinks (see
http://www.stearns.org/freedups/ )to shrink space requirements, rsync for
fast backups, ssh for authentication and complete encryption....
	Cheers,
	- Bill

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On Sat, Feb 02, 2002 at 04:27:22PM +1030, Richard Russell wrote:
> > I think what you want is a covered by LVM snapshots:
> > 
> >
> http://www.sistina.com/lvm_howtos/lvm_howto/Taking_a_backup_using_sna.html
> > 
> > The scenario you mention isn't quite the same as that in the HOWTO but
> > you can use it in a similar way by making a snapshot of the /home
> > filesystem each evening and mounting that as a backup.
> 
> Nice. I was completely unaware of the snapshot facility of LVM (and
> indeed, unaware that LVM was usable on Linux)...
> 
> Thanks... How would this kind of thing compare against a generic COW
> driver, for things like performance, stability, and likelyhood of being
> usable shortly?

It's not a generic COW driver in that the volumes you snapshot must be managed
by LVM already but it is stable and works now. It's in the standard 2.4 kernel,
all you need to do is download the tools from http://www.sistina.com/lvm.

Performance is OK for a single snapshot but can get a bit sluggish if you have
multiple snapshots of the same volume - this is being addressed in a new LVM
implementation we are currently working on.

It's probably worth pointing out that it actually works the other way round to
the UBD COW system. So you take a snapshot of a volume, and mount that
somewhere else. That snapshot volume then does not change even when the
underlying volume does. It does this by taking a copy of the changed data from
the original volume in the snapshot COW data. Because of this you have to be
very careful to allocate enough space to the snapshot to hold all the potential
changes to the original.

patrick