Re: [Vserver] A possible new idea

From: Stephen Harris <>
Date: Thu 11 May 2006 - 04:20:01 BST
Message-ID: <>

On Thu, May 11, 2006 at 12:35:38AM +0200, Herbert Poetzl wrote:
> why would somebody want to _share_ the host files with
> the guest, instead of having a separate filesystem for
> them?

This is actually how Solaris 10 zones work. In a Solaris 10
zone the filesystems /usr /bin /lib and so on are read-only loop-back
mounts to the host OS. It makes the guest a lot smaller as a result.
Pretty much most of the overhead of a guest ("zone" in Solaris terms)
is the local files in writeable filesystems to ensure OS stability
(eg /var/sadm for package maintenance).

You don't have to worry about patching each guest because each guest
is using the host OS; patch the host, reboot the guest and it's
automatically patched. Yes, this requires native OS support (eg the
patch utilities need to know that a guest exists and so updates it's
package state files; the patch _contents_ would appear automatically as
a result of the loopback mounts; it's merely the package state files that
need updating).

The vserver vhashify solution is an attempt in the same direction but
because it uses hard links it's not necessarily so space efficient
(you need at least one copy of the guest files in the /vserver tree,
whereas a read-only loopback mount doesn't need it). The vserver solution
allows each guest to modify the files as needed (break the immutable hard
link, create a new file) whereas Solaris 10 zones are read-only; you can not
modify /bin/bash in a zone(guest).

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