[OT]: bash or any other $favourite{shell}? [was: Wish list]

[paddy]

On Sun, Jun 11, 2006 at 06:09:38PM +0000, Peter Corlett wrote:
> Chris Benson <chrisb at jesmond.demon.co.uk> wrote:
> [...]
> > Ah, that may reduce my interest in UML before the book even arrives :-) I
> > was hooked by the promise of UML sharing the host's o/s image, but that
> > uses Copy-on-Write ... so I'm unclear whether local changes in the child
> > will be visible to the host.
> 
> Well, it is possible that UML does have the capability, but it seems
> unlikely. I have no experience of it to say one way or the other.
> 
> Basically, virtualisation falls into two camps:
> 
> a) chroot-on-speed, e.g. linux-vserver, FreeBSD jails, Solaris zones.
>    Everything runs under the same kernel instance. It's a very lightweight
>    scheme. Linux-vserver suffers from some interesting gotchas due to the
>    single kernel instance, and I imagine the others are similar.
> 
>    Due to the single kernel instance, there's only one thing accessing the
>    filesystem so the controlling/root server can access the filesystems.
> 
> b) Individual kernel instances that run separately, e.g. UML, Xen, VMWare.
>    Everything looks and acts like a physical machine. It's relatively
>    heavyweight but the extra separation can make this worthwhile.
> 
>    Because each kernel has its own buffer cache et al, it's impractical to
>    mount filesystems in use by another virtual server except over something
>    like NFS.

Although lvm snapshots might be useful in such a context. 

The real question is what do you want the visibility for ?

Clustered fileystems and nbds, like drbd, also come to mind, but I can't
immediately imagine why choose them over the chroot-on-speed option, but 
it comes to mind in the context of either test or vm migration.

Regards,
Paddy
-- 
Perl 6 will give you the big knob. -- Larry Wall