any downside to 100MB Transport Dumpster


After reading about Exchange 2010 SP1 DAG, Transport Dumpster and AutoDatabaseMountDial I have decided I'd like to use a high transport dumpster setting of between 60-100MB.  Is there any down side, performance or recoverability wise to increasing the default this much?  Our message size limit is 30MB and I realize the recommendation is 1.5 x that size, but for added insurance during an automatic failover, I want the larger size.  Is there a down side?
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Jessie Gill, CISSPTechnical ArchitectCommented:
I don't believe there is any real downside to doing what you are doing, but the transport dumpster has changed a bit in 2010, it no longer holds messages in the dumpster waiting for the size limit to be reached to truncate the dumpster.  The Dumpster in 2010 now receives feedback from the replication pipeline to determine which messages have been delivered and replicated.  Once the message has been committed to all copies it auto truncates the message.
JohnDemerjianAuthor Commented:
can you describe precisely under what circumstances a message is at risk for being lost?  and does being lost mean no NDR to the sender?
Jessie Gill, CISSPTechnical ArchitectCommented:
Well I have not really heard of messages being lost it is possible but because the dumpster now waits for information from the replication pipe line to confirm the message has been committed to the copy database, I don't really believe you will run into this issue.  Also I do believe their will be no NDR if a message is lost.  I have been running exchange 2010 for about 3 months I migrated from 2007 recently and we have over 5k user mailboxes and I have not experienced any complaints of lost messages.  The way the DAGs work now  the copy's are always getting the transactions from the active copy, so if your primary database failed and a copy had to become the active I do not believe you will lose any emails due to the dumpster not  deleting the message since the copy had not committed it, if the new active db is missing messages the dumpster should have them as they were not committed.  I have done testing in my production environment by turning off mailbox servers and making the copy active and I have never heard of any issues regarding lost email.

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JohnDemerjianAuthor Commented:
Let's say that between the time a db goes offline on one server and online on another, the elapsed time is 10 seconds.  During that time I receive 50 megs of email destined for mailboxes on that db.  Where does that 50 meg sit while it waits for the db to come online?  Does it sit in a delivery queue?  Because I can't find info that explains how long mail will sit in queue.  All I can find is info about the shadow retry feature that tries a different hub transport, which I understand. But if the mailbox is offline trying a different path to it is pointless.

So what does the 50 meg of mail do for 10 seconds?

Thanks for working this through with me...
Senior IT System EngineerIT ProfessionalCommented:
ok, if my Exchange Server 2010 not using DAG in the two mailbox servers, how much is the size for the ttransport dumpster size to allow me send and receive email with 50 MB attachment ?

[PS] C:\>Get-TransportConfig | fl *Max*
MaxDumpsterSizePerDatabase      : 50 MB (52,428,800 bytes)
MaxDumpsterTime                 : 7.00:00:00
MaxReceiveSize                  : 50 MB (52,428,800 bytes)
MaxRecipientEnvelopeLimit       : 5000
MaxSendSize                     : 50 MB (52,428,800 bytes)
ExternalDsnMaxMessageAttachSize : 25 MB (26,214,400 bytes)
InternalDsnMaxMessageAttachSize : 25 MB (26,214,400 bytes)

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