RE: fault tolerance needed in exchange 2003 enviro nment

  • From: "Mulnick, Al" <Al.Mulnick@xxxxxxxxxx>
  • To: "[ExchangeList]" <exchangelist@xxxxxxxxxxxxx>
  • Date: Fri, 18 Jun 2004 11:08:19 -0400

Fault tolerance?  No.  None of that there. 

Here's why: The ADC is only need to join the 5.5 and Active Directory
directories.  Truth be told, you could likely live without it until you can
build a new machine to take over for it's CA's which would then specify that
the new host will pick up where the last one left off; no full resynch

As for your Exchange/Active Directory, you have no fault tolerance there
either. If you lose Exchange, there is nothing to take it's place.  If you
lose the DC, Exchange goes with it.  Since Exchange is loaded on the DC, it
also won't look for other DC's should you deploy them.  Active Directory is
not fault tolerant either, since you only have one DC (all your eggs are in
one basket so to speak).

Typically it helps to look at it in infrastructure layers, but first let's
get a common understanding:
Fault tolerant - able to withstand a fault and continue to function without
interruption and without manual effort.
High availability - able to withstand a physical hardware fault and continue
to function with minimal interruption and minimal manual effort.
1) physical - is your network fault tolerant?  If not, no sense in going
past here is there?  
2) Environmentals - Is your datacenter fault tolerant?  If not, maybe fault
tolerant is not what you really want.   If the datacenter goes away and you
have no recovery, everything that depends on it will also be inaccessible.
3) name resolution - is your name resolution infrastructure able to
withstand the loss of a component?  
4) Hardware - is your hardware fault tolerant?  Not just fault tolerant
components such as redundant power supplies, but is it fault tolerant like a
hymalaya type hardware setup?  If not, maybe you really want high
5) OS - is your operating system fault tolerant?  Not unless you have a
custom build it's not.  It may be highly available, but it's not fault
tolerant since failure of the dependent components will result in loss of
6) application - if your other components line up with fault tolerance, is
your application setup for fault tolerance?  In the case of Exchange, there
is no fault tolerant, but there is highly available in the form of clusters.

If you want more resiliency out of your setup, start by setting up
additional servers: a second DC and another backend exchange server as a
part of a cluster. You want to get to a level where you have your Exchange
server on it's own cluster, and you have DC/GC's that are only DC/GC's. In
this situation, if you lose a DC, you still have another until you can get
the original back in service.  If you lose a single Exchange host due to
hardware, you have an additional to take it's place.  If you lose the ADC,
stop making changes to the directories and find a desktop to take it's place
(a decent one though).  That'll give you hardware high availability.  To
finish this out, you need to have a datacenter elsewhere (in case of natural
disaster) with the other DC/GC or possibly a third, and the other Exchange
node of the cluster. I think that's excessive, since it's likely if you have
only one site that your workstations are there as well.  And if you have no
workstations to access the mail, what's the point, right?

Good luck.  Be sure to check out the Microsoft whitepapers on disaster
recovery for more information


-----Original Message-----
From: mohit mehrotra [mailto:moh_meh@xxxxxxxxxxxxxx] 
Sent: Friday, June 18, 2004 5:17 AM
To: [ExchangeList]
Subject: [exchangelist] fault tolerance needed in exchange 2003 environment


I have installed windows 2003 DC loaded with exchange 2003, also installed
windoows 2000 adv.ser. as ADC with exchange 2000 in same forest.

 I want to clear abou two points

1. whether this is appropriate system to provide fault tolerance.

2. In case of problem with my schema master server(2003) can ADC will take
charge for exchange (i.e. mailboxes etc.) after making a change in public IP

Kindly suggest any other thing viable for this scenario.


Moohit Mehrotra

Moohit Mehrotra

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