Re: [Xen-users] Multiple Domains Sharing Root System

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

>
> * ...NFS exporting a read-only copy of /usr.  This is usually your largest
> partition where most updates occur.  Well-written programs will not require
> /usr be mounted read-write and you should be able to export at least that
> partition.  You can do updates very quickly.  This is the direction I want
> to go.
>
You could also read-only share a block device for /usr between all domains.  
This gives good performance and you still only have one image of the 
filesystem.  The trouble is that with block-level sharing you can't update 
the filesystem whilst there are more than one domains accessing it :-(

I used to do this, now I just have multiple complete installs.

There are a number of people here working on other solutions for filesystem 
sharing that may be better in some circumstances.

Cheers,
Mark


> You could even use thin-client network boot technology so that your domains
> don't use *any* hard drive space.
>
> You can test your app by installing a new installation of linux or unix and
> giving /usr its own partition.  Install the program you want to test.  Edit
> /etc/fstab and give the /usr partition the ro flag something like this:
> LABEL=/usr  /usr  ext3  defaults,ro  1  2
> Remount /usr:
> mount -o remount /usr
>
> Or do it without editing fstab (does not persist over reboots):
> mount -o ro,remount /usr
>
> Then run your app and see if it bombs.  If it works, you can use a
> read-only NFS-mounted /usr partition.
>
> Note: This only shares /usr.  If you install an update that modifies a file
> under /etc /var or /boot you will need to manually copy those updates.  It
> is not wise to share /etc or /var (they are usually thought of as the place
> where system-specific and variable data lives) and /boot /sbin and /lib is
> usually needed before NFS filesystems can be mounted (usually).  So any
> updates to these partitions must be done manually.
>
> I suppose the main server could run an update and then the NFS clients
> could run the same update, ignoring any /usr "read-only" errors.  Seems
> like it would work, but then that takes the same amount of time as updating
> individual servers.
>
>
> Or you could just...
>
> * ...bite the bullet and do it the old-fashioned way.  A well-tuned OS
> doesn't take up much room compared to swap and data.  Most of my installs
> are a few hundred MB (I kill the documentation and only install what I
> need).  The average Xen system probably has a dozen domains, so that's
> around 10GB.  That's nothing with today's drives.
>
> Doesn't give you quick-update ability but you can use something like yum or
> apt.  I've installed both yum and apt servers; they're no big deal.
>
> Hope that helps!
>
> CD
>
> You have to face a Holy God on Judgment Day. He sees lust as adultery
> (Matt. 5:28) and hatred as murder (1 John 3:15). Will you be guilty?
>
> Jesus took your punishment on the cross, and rose again defeating death, to
> save you from Hell. Repent (Luke 13:5) and trust in Him today.
>
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>
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