Re: mirrored machines via network

Jauder Ho (
Fri, 1 Nov 1996 14:23:27 -0800 (PST)

Try looking at Auspex's ServerGuard.


On Fri, 1 Nov 1996, James R. Leu wrote:

> First off please let me apologize for my lack of kernel programming
> knowledge, this is my first venture into kernel space. My basic goals of
> this letter are 1) a reality check and 2) to obtain a list of resources of
> where to look or what to read to get me started.
> As my title below states I'm in charge of administrating all the network
> operations of a small ISP. I am looking into ways of implementing redundant
> servers. By this I mean two machine that are exactly the same as far
> as services provided, and data stored. There only deviation would be the
> IP address assigned to it. My example will hopefully reveal why I want to
> achieve this.
> The idea I have, necessitates two main developments. The first of which is
> a "intelligent" name-server. I have begun development of this already. I have
> started by using th bind-4.x.x source. The end result will hopefully be a
> name-server that checks if a machine is responding, before it gives out the IP
> address. The second of which is the "mirrored machines via the network".
> Because of my limited knowledge of kernel I/O I'm not really sure how to
> implement such a driver/service. My initial looks into the I/O subsystem led
> me into the drivers/block directory of the Linux kernel source. I look at hd.c
> and could understand what was happening, but I don't understand how it fits in
> to the whole scheme of things.
> The best way to illustrate how the entire system would work would be to give an
> example. I will refer to the primary machine as machine A, and the backup
> machine as machine B. There is at least a third machine on the network, and
> this operates as the primary DNS for the network. Under normal situations
> (ie no failed hardware, no kernel panics :o) machine A response to all WWW
> services all e-mail services, and all authentification requests and usage
> accounting (via RADIUS). The machine also serves shell logins. During this
> time machine B needs to constantly be updates to account for changes in web
> pages, changes in passwords, in general all changes to the file system on A need
> to be duplicated on B. The reason it needs to be duplicated arises when
> machine A blows up. At this time the primary name server would notice that
> machine A is not responding correctly. It would switch its internal tables for
> machine A and now point them to machine B.
> I do realize there are many areas that need to be worked out. The least of
> which is how to determine if a machine is no longer responding, but I hope with
> some input from this community, to be able to overcome each problem and form
> a truly reliable solution. I welcome all responses/tips/hints/flames.
> Last but not least, if anyone has seen this or anything similar, please let me
> know. I looked long and hard for something similar, but I'm sure my search
> was not entirely exhaustive. Also I know my view of this may be naive, so
> please do enlighten me.
> James
> --
> James R. Leu
> Network Administrator
> CORE Digital Communication Services

.sig under construction