RE: Exchange Server Redundancy

  • From: <paul_lemonidis@xxxxxxxxxxx>
  • To: "[ExchangeList]" <exchangelist@xxxxxxxxxxxxx>
  • Date: Tue, 9 Mar 2004 16:50:24 -0000

Hi Al

There seems to be something missing here unless I am mistaken. A cluster only 
has one set of shared drives. Hence why you use multiple RAID drives or arrays 
with multiple controllers. Thus there are no replication issues etc. This is 
also why failover can be so fast as the secondary machine/node (one is the 
primary node, one the secondary as you probably already know) is already 
on-line and using the same disk drives.

The software solution is not clustering as it does not use shared drives 
between the two nodes. It is a co-standby server solution and this is not the 
same thing at all. Instead the two nodes have independent drives that then must 
be replicated in real time. This is a big overhead and hence a poor mans 
solution at best. Also, of course, there can be well be replication issues as 
you correctly point out.


Paul Lemonidis.
  ----- Original Message ----- 
  From: Mulnick, Al 
  To: [ExchangeList] 
  Sent: Tuesday, March 09, 2004 4:36 PM
  Subject: [exchangelist] RE: Exchange Server Redundancy

  In a roundabout way, that's what I'm trying to get to.  I realize there are 
hardware solutions that do the same; they replicate writes (really they 
bifurcate the write to disk) so you can have geoclustering solutions.  But I'm 
trying to figure out how these bright programmers figured out a way to protect 
the application data and provide a six second failover.  I'm concerned that 
such a solution would be a "poor man's" cluster at best, and a data integrity 
nightmare at worst.  I don't see how the fast failover claim can work with the 
application nor how it is better than the MCS solution offered by the vendor of 
the application (concern for the third-party support comes into play here), but 
I have an open mind and if progress has been made, I'd like to educate myself 
on it.

  So far I don't see how the solution could be better, but I'm certainly 
interested to hear.

  From: paul_lemonidis@xxxxxxxxxxx [mailto:paul_lemonidis@xxxxxxxxxxx] 
  Sent: Tuesday, March 09, 2004 11:21 AM
  To: [ExchangeList]
  Subject: [exchangelist] RE: Exchange Server Redundancy

  Hi all

  Sorry if I am missing something here but since when is a pure software 
solution that replicates an entire drive going to offer perforamnce anywhere 
near that of a cluster using shared drives. This seems nothing more than a 
co-standby server solution like say Vinca? Rather than a single shared drive it 
runs huge amounts of replciation between dupliacte drives on duplicate servers. 
I can actually see you paying more for an inferior solution from what I have 
seen so far.

  Hardware clustering is far more resilient if done correctly but it does come 
at a price, of course. At the end of the day you get what you pay for.


  Paul Lemonidis.
    ----- Original Message ----- 
    From: Mulnick, Al 
    To: [ExchangeList] 
    Sent: Tuesday, March 09, 2004 3:23 PM
    Subject: [exchangelist] RE: Exchange Server Redundancy

    I never considered MCS to be more difficult than adding a third-party app.  
Is that all it does?  How does it make the recovery so fast?  How does it check 
for db consistency?  

    From: Tiago de Aviz [mailto:Tiago@xxxxxxxxxxxxxxx] 
    Sent: Tuesday, March 09, 2004 9:17 AM
    To: [ExchangeList]
    Subject: [exchangelist] RE: Exchange Server Redundancy

    It is much simpler because it can be implemented on a single day, it 
replicates data on the bit level, it's a cheap software, and if you want, you 
can user a slower machine or any other machine for redundancy.


    No, while Brightstor is replicating, it doesn't know if the file is a 
database or a Star Wars movie. It's all the same for him.


    Tiago de Aviz


    (41) 340-2363


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