[Info-vax] free shell accounts?

[Jan-Erik Soderholm]

Stan Radford skrev den 2015-01-22 15:27:
> On 2015-01-22, Phillip Helbig (undress to reply) <helbig at asclothestro.multivax.de> wrote:
>> 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,
>
> What does that mean actually? Does that mean they share physical disks
> because they all have physical connections or something else?

That is a must if you do not want the disk access beeing
dependent on any specific single VMS system.

> If it's multiple boxes connected to one or more disk arrays that
> make sense. If not I don't understand how it can work.

Correct (both).

>
>> is working on.  One or more nodes can go down, for planned or unplanned
>> reasons, and the cluster continues to exist.
>
> As long as they're all physically attached to the same drives. But if
> they're attached to network drives and the owning box goes down then there's
> a problem.

A "network drive" of today is usualy served from some NAS or SAN
type of storage. A VMS system *can* also serve one or more of its
local disks to the cluster (using MSCP), but then you are depending
on that single system for disk connectivity.

http://en.wikipedia.org/wiki/Mass_Storage_Control_Protocol

>> 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.
>
> I don't understand how this can work until somebody explains the above
> issues!

Was the above clearifactions enough? :-)

The "best" solution is of course if each VMS system has its
own independant connection to the storage/disk volumes. But
it is not an absolute *must* to run a VMS cluster.

Jan-Erik.

>
> Stan
>