Re: [Xen-users] How to share data between guest domains

[Brock Edward Palen <brockp@xxxxxxxxx>]

Todd D. Esposito wrote:

> On Sun, March 19, 2006 5:59, Richard Jones said:
>  
>
> > On Sat, Mar 18, 2006 at 09:00:28PM -0600, Todd D. Esposito wrote:
> >    
> >
> > > However, on that note, I wonder if you could mount the same file system,
> > > say something like /usr, into multiple domU's READ ONLY.  That could
> > > certainly save some trouble when updating applications, etc.  Anyone
> > > tried
> > > it?
> > >      
> > This would only work if the disk is read-only *and* never changes
> > while the machines are up.  The reason for that is that the kernel
> > keeps disk blocks cached in memory, and assumes that the disk won't
> > change randomly underneath.  If they did, then it would lead to a
> > situation where the kernel is randomly using a mix of stale (cached)
> > and fresh blocks.
> >
> > In other words, if you wanted to upgrade parts of /usr, you'd need to
> > shut down all your domUs, carry out the upgrade operation, and then
> > boot them up again.
> >    
> This is in line with my first instinct, but I'm one of those "try it
> anyway, it might work" kinda guys, so thanks for saving me some lab time.
> ;-)
>
>  
>
> > Over here all our domUs have separate partitions.  You only need max
> > 3G for a complete Debian with plenty of packages, and how much does 3G
> > of disk cost these days?  The task then moved to automating sysadmin
> > as far as possible -- see cfengine and apt-cron.
> >    
> Sure, disk is cheap; my aim was really to reduce sysadmin time/overhead. 
> I've glanced over cfgengine, and will likely go that way as my number of
> systems (and domU/system) grows.  apt-cron won't do it for me, as I'm on
> Gentoo, but there are no shortage of similar tools.  Thanks for the
> recommendations.
>
> - Todd
>  
Todd,
I use xen with gentoo also one thing I do and i know is documented in 
some gentoo doc's is i only use one portage tree
I NFS export /usr/portage read-only and /usr/portage/distfiles rw to all 
my dom'U's from dom0.  When i sync I sync dom0 like normal
emerge --sync
and the domU's i
emerge --metadata

This only saves about 1G/domU  but its nifty to only sync once from 
rsync.gentoo.  I used to use a local rsync mirror
Brock

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