From: Herbert Poetzl (herbert_at_13thfloor.at)
Date: Tue 06 Jan 2004 - 06:04:49 GMT
On Mon, Jan 05, 2004 at 09:56:00PM -0500, Gregory (Grisha) Trubetskoy wrote:
> Hi -
> I've been using FreeBSD jail for a while, but am new to Vserver, which
> seems like cool stuff, I'm thinking of using it for hosting customers.
> I've got a few questions for the list.
> 1. On FreeBSD, a common way to share files across virtual servers is to
> mount them using unionfs read-only, which allows basically one part of a
> file-system to be mounted in another place.
> The idea is to then symlink all important files shared across jails to
> that mount point to save space. The user of the virtual server can then
> delete the symlinks as he wishes to replace them with real files (which
> will take up more space).
> First, there doesn't seem to be anything like unionfs on Linux (mount
> --bind doesn't really allow read-only mounting). I'm thinking NFS might do
> the trick, though.
there is a patch, I did some time ago, and tried to get
into Marcello/Andrew kernel, but it wasn't accepted yet,
which allows ro --bind mounts ...
and there is the concept of immutable but unlinkable
shared files (called unification) which might be
more powerful than a unionfs in some cases ...
> Has anyone tried a set up like this, or are people generally happy with
> using the hard links as described in the vserver docs? It seems to me
> there is an advantage to symlinks in that you can modify the files that
> the links point to and the change is immediate across all virtual servers.
> Plus, symlinks make it a bit more apparent to the user on what's going on
> (although sometimes you may not want this) and make space accounting
that is not exactly the idea behind that, but you'll
see if you give it a try ...
> 2. Another thing common in the BSD world is to place jails into vnode file
> systems - i.e. a filesystem mounted from an image file, same as the mount
> loopback on Linux. This is a pretty efficient way to restrict disk space,
> but, of course you won't be able to use hard links in this set up since
> hard links cannot cross filesystems.
> The only other alternative to restricting space seems to be the context
> quota patch - does this work reliably? What does df show from within the
yes, if done properly, this does work reliably, and it
shows you exactly what you want to see there ;)
> Basically I'm a bit torn between trying to set up virtual servers using
> the ways I learned in FreeBSD - loopback filesystem, nfs mounted read-only
> directory with symlinks, or giving up on that idea and just doing using
> the context quota and the hard links as described in the vserver faqs.
> Has anyone gone through this experience?
yup, just visit the irc channel an have a talk with
some folks there ...
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