There are several components within Exchange 2010 that administrators may not come across unless they are troubleshooting very specific issues, or reading level 400 texts. This is the first post in what may become a series on some of the deeper internal workings of Exchange 2010. In this first post, I want to introduce you to the Transport Dumpster.

The Transport Dumpster is just one of the inner components of Exchange that sits quietly and unobtrusively on a Hub Transport server, helping to protect data in the event a server experiences any type of failure that would otherwise lead to a loss. You may not notice it, but you will be glad it is there, and in certain circumstances, you may want to adjust its default settings.

The Transport Dumpster first appeared with Exchange 2007, and is a queue that can be found on every Hub Transport server that resides in an Active Directory Site that contains a DAG. It helps prevent loss of data sent from the Hub Transport Server to a Database Availability Group when something fails that would result in a lost message. There is one Transport Dumpster per replicated database.

When a message is sent from a Hub Transport server to a Mailbox server, the messages is stored in the Transport Dumpster queue for the DAG until the Hub Transport server receives a notification that the transaction logs for a particular message have been replicated to all copies of the DAG and inspected by the Mailbox server. Once every DAG member confirms that the message logs have been committed, the message will be purged from the queue, but if a DAG member either does not acknowledge the logs, or reports that the logs failed, the Transport Dumpster can resend the information to the DAG member.

The Transport Dumpster stores messages for a period of time controlled by the MaxDumpsterTime setting, which is seven days by default, or when the maximum size of the queue is reached. The default for that is 18MB, but Microsoft recommends that this is set to 1.5 times the maximum message size limit. Whenever one or the other limit is reached, messages are purged on a first-in, first-out basis. You can view the current settings using the EMS and running the command

Get-TransportConfig | fl *Dumpster*

You can adjust the parameters for the Transport Dumpster by using these commands in the EMS. In these examples, we set the size to 30 megabytes, and the lifetime to 4 days.

Set-TransportConfig -MaxDumpsterSizePerDatabase 30MB

Set-TransportConfig -MaxDumpsterTime 4

You can enter the size specifying MB for megabytes, or you can enter a value in bytes. The time can be entered in EnhanceTimeSpan format, but a simple digit will give you days.

It is important to note that the Transport Dumpster does not protect against data loss during a failure should the message be destined for either a public folder, or for a mailbox database that is not a part of a Database Availability Group. It can only protect replicated mailbox databases.

If you found this post interesting/useful, please leave a comment to let me know, or tweet it if you’d prefer. If there is enough interest, I will continue the series on the inner workings of Exchange.