From: s5udtg@fnma.COM (Doug Griffiths)
Subject: Re: Having mirror servers on a network
Reply-To: s5udtg@fnma.COM
Organization: Fannie Mae
Date: Wed, 18 Nov 1992 23:24:07 GMT

>From: s5udtg@colorado (Doug Griffiths)
>To: lim@telerobotics.jpl.nasa.gov (David Lim)
>Subject: Re: Having mirror servers on a network
>Cc: 
>
>We have just purchased two Sun 690 MP servers and are in the process of
>bringing them up. What would really be nice is if the machines can become
>mirrors, so that if one server goes down, all the client machines do not have
>to go down. We are using NIS, automount, and storing common utilities on the
>server (e.g. gnu emacs). As an added complication, the two servers are
>on different subnets, but the machines will be setup as gateway to each other.

The answer is Sun's IPI Dual Port 1.0 software & DiskSuite 1.0 software, and
to hire Fusion Software (Sun recommended) to write your fail-over scripts.  
We are running 6 sets of High Availability servers (4/690's) here, with varying
success. Apparently, we were one of the first sites to contract Sun (Fusion) for 
this type of setup.  

A short description of this setup :

Two servers, physically accessing (cabled to)the same drives (dual-ported drives), 
and connected through a "service" subnet and a "front" subnet.  Only one 
server can access the drives at any one time; therefore one server is configured
as a "primary" server and is accessed by users/clients through a pseudo name. 
Each of the disks on both servers are mirrored to provide recoverability from
disk failures.  If the "primary" server fials, manual (or automatic, we do it
both ways) cutover involves unconfiguring the "primary" server and configuring
the backup server as "primary".

This of course wouldn't work as you've described your environment, and to answer
your other questions:

>- The two servers would have their own set of files (e.g. their own identical
>  copies of gnuemacs). No cross mounting between the two machines

Not possible, unless you set up two different copies on one machine.  Remember,
you may own two 4/690's, but in the dual-port configuration you have only
ONE pseudo machine.

>- use the same domainname

Oh, definately.  Remember, you are accessing only ONE MACHINE.


- The two servers would have their own set of NIS file, i.e. each one will be
  a NIS master. The reason for this is the automounter consults the NIS for
  the machine to mount from. Thus it would be setup such that the NIS files
  on server1, would automount from server1, and NIS files on server2
  would automount from server2. Thus if client1 was picking up NIS from
  server1, it would mount server1 directories. If server1 goes down, client1
  will automatically pick up server2's NIS, and then eventually the automounter
  will mount server2's directories. Is this doable in practice? Or would I
  have to manually reboot every client associated with server1? I know that
  switching NIS servers is relatively quick, and automounted directories, if
  not used will be unmounted after a few minutes. But if a user was in a
  automounted directory, then would the client would simply hang?

Not possible.

- how about mail? Can mail be centrally located in this scheme? If client1
  has server1 as its central mailhost, if server1 goes down will client1 go
  down? Is it possible to soft mount the /var/spool/mail directory to allow
  client1 to continue to run? 

This would work, although not exactly as you've described it.

   
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