[Beowulf] Compute Node OS on Local Disk vs. Ram Disk

[Eric Thibodeau]

Bogdan Costescu wrote:
> On Tue, 30 Sep 2008, Eric Thibodeau wrote:
>
>> This has given me much flexibility and a very fast path to upgrade 
>> the nodes (LIVE!) since they would only need to be rebooted if I 
>> changed the kernel. I can install/upgrade the node's environment by 
>> simply chrooting into it and using the node's package manager and 
>> utilities as if it were a regular system).
>
> Only the first is an advantage of using NFS-root; the second is shared 
> by most methods that use a node "image". 
More or less, NFS-root changes are "propagated" instantly, most other 
approaches require a re-sync. Another way to see this, the NFS root 
approach only does changes on the head node and changed files don't need 
to be propagated and are accessed on a as-needed basis, this might have 
significant impacts on large deployments....not that I suggest that they 
use this approach ;)
> However random installations or modifications of configuration file 
> within the chroot become very difficult to reproduce when you build 
> the next node "image" 
Document document document...which no one does...but document.
> - either scripting everything or using cfengine/puppet/etc. can save a 
> lot of time in the long run, despite the initial effort to set up.
I'll take your word for it that they have a version tracking mechanism.
>> But I am in a special case where, if I break the cluster, I can fix 
>> it quickly and I always have a backup copy of the boot "root" image 
>> ready to switch to if my fiddling goes wrong.
> Why not keeping several "images" around and only point the nodes to 
> mount the one considered current or "good" ?
Well, that's what I meant... probably not clearly. ;)

Eric