Re: Integrate Knoppix in Debian (was: Re: Debian Enterprise?)
On Wed, Nov 26, 2003 at 06:18:03PM +0100, Goswin von Brederlow wrote:
> Matt Zimmerman <mdz@debian.org> writes:
> > So am I to understand that you plan to use device-mapper snapshots in order
> > to provide copy-on-write at the block device level in order to implement
> > this? If so, this is interesting. I assume you will use a RAM disk for
> > writable storage? What filesystem will you use?
>
> Yes, thats exactly how it works. One device for the loopback file, one
> for the ramdisk/tmpfs storage and a copy-on-write snapshot combining
> those two into the real root device.
>
> Recent kernels allow using loopback files on tmpfs. Older kernels need
> to use one or more ramdisks.
Hmm, so a loopback file on tmpfs could be sparsely allocated, and tmpfs
would dynamically allocate memory as it grew. Very nice.
> As filesystem I only used ext2. But device mapper provides a normal block
> device like any other. Only think to note is that using a journaled
> filesystem like ext3, xfs or reiserfs might not be the best idea since the
> journal will fill up 32 MB (or whatever the fs has) of ram with no
> benefit.
Correct, a journal does not make sense. I do wonder, though, whether
particular filesystems would attempt to minimize resource consumption in a
situation like this, by reusing deleted blocks rather than allocating new
ones, something opposite to what jffs2 does.
--
- mdz
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