Microsoft tech support suggests making changes to the “MSExchangeMailboxReplication.exe.config” file located at “C:\Program Files\Microsoft\Exchange Server\V15\Bin”. The values to look at, along with their default settings are:
MaxActiveMovesPerSourceMDB=”20″
MaxActiveMovesPerTargetMDB=”20″
MaxActiveMovesPerSourceServer=”100″
MaxActiveMovesPerTargetServer=”100″
MaxTotalRequestsPerMRS=”100″ExportBufferSizeKB=”512″
We typically like to set these values so that about 10 mailboxes can be moved simultaneously. The ExportBufferSizeKB we’ve used in the past is “10240”. The Exchange Mailbox Replication Service should be restarted after these changes.
The other suggestion Microsoft has made is to disable content indexing on the target database so that the search index scanner isn’t overwhelmed by all the new messages needing to be indexed. You’ll want to set it back once the migration is complete.
Set-MailboxDatabase “DB1” -IndexEnabled:$False
In our experience however, these first two suggestions do NOT have tremendous impact on the overall speed. The following two options have proven to be the most effective for us.
Use the “-priority emergency” parameter on the mailbox moves. This will give the move the highest priority in the MRS queue. For example:
New-MoveRequest -Identity “user@domain.com” -TargetDatabase “DB1” -Priority emergency
If the priority flag and the MRS config editing doesn’t make the moves fast enough for you, then disable MRS throttling altogether! To do this, change the “MRS” REG_DWORD key from 1 to 0 under this registry path:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\MSExchange ResourceHealth
Then restart the Exchange Mailbox Replication service. Now your mailboxes will move without any throttling policy. Once the mailbox migration is complete change the value back to 1 to re-enable MRS resource monitoring.
Try one or a combination of these in your environment and see what works best for you.
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