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JerryJay

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Don't understand how Shadow Redundancy in Exchange 2010 work

I've reading Shadow Redundancy article from Microsoft site:
http://technet.microsoft.com/en-us/library/dd351027(EXCHG.140).aspx

Question 1: In the document, it gives an example of "Multiple Hop Scenario", the step 3 says:

3.The Chicago hub queries the New York hub for discard status and receives the discard notification for the message. At this time, it can remove the shadow message from its database. Whether the message was delivered from London to Dublin doesn't have an impact on when the Chicago server deletes the shadow message.

Why "whether the message was delivered from London to Dublin doesn't have an impact on when the Chicago server deletes the shadow message"???

It seems to comflict with the Microsoft definition of "Shadow Redundancy" saying "With shadow redundancy, the deletion of a message from the transport database is delayed until the transport server verifies that all of the next hops for that message have completed delivery"

it clearly says that the deletion of a message until verifying that ALL of the next hops for that message have completed delivery!

Anyone can help to explain that?

Thanks in advance,
Jerry
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thanks to all above comments, now I understand "shadow redundancy is not guaranteed delivery from source to destination, just from hop to hop" as endital1097 explained

But...

Akhater says: "With Exchange 2010 Microsoft tries to make hardware "disposable" meaning that any failing hardware can be replaced without any impact or data loss"

The document talked about an example of an Hub trying to deliver a msg to an Edge, after delivery, it query the Edge for confirmation of delivery, but failed to talk to the Edge, it then resent the msg from Shadow queue to another Edge for delivery. sounds great!!! but what about in a senario that the very first Hub server picks up whole bunch of messages from a Mailbox server, but before it tries to deliver them, it fails. will that cause any data lost? it answer is YES, how can Microsoft make hardware "disposable".

My understanding is the shadow Redundancy is for data protection between hub to hub/edge communication, not for mailbox to hub communication. If a hub fails, there will be data lost if it didn't deliver msgs which it picked up from mailbox servers. this can be very common, i think, when a hub fails
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many thanks to Akhater and endital1097. good answers! appreicate all your help here.