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

[Richard Jones <rich@xxxxxxxxxxx>]

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.

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.

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
Team Notepad - intranets and extranets for business - http://team-notepad.com

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