[Info-vax] free shell accounts?

[Phillip Helbig undress to reply]

In article <m9q6li$5er$1 at speranza.aioe.org>, Stan Radford
<sradford at noemail.net> writes: 

> I don't understand what a cluster does. If they don't have shared disks
> somewhere wouldn't they have to have multiple copies of everything? How does
> a cluster still remain usable if you are editing a file and the machine the
> file lives on fails? I can see for serving applications a cluster would be
> great but I don't understand how it helps development users. And even that
> would seem like it would take a lot of planning and wouldn't just automatically
> "work" because of the need for shared storage somewhere.

There are several possibilities, but probably most clusters have all 
disks mounted on all nodes, and common "system files" such as SYSUAF.  
The number of system disks can vary.  (Many: more work but more 
flexibility and vice versa.)  This allows one "virtual machine" to 
become more powerful if needed.  Also, it doesn't matter which node one 
is working on.  One or more nodes can go down, for planned or unplanned 
reasons, and the cluster continues to exist.

Of course, if a node goes down, the processes running on it will.  When 
editing a file, then obviously you can't just continue editing 
elsewhere.  All you have to do, though, is log in again (things can be 
set up so that there is a virtual address for the cluster) and type 
EDIT/RECOVER to get back to where you were when the crash occurred.