EOL - Troubleshooting Exchange Online Mailbox Migration Speeds

Working for a client we run into numerous issues where we were seeing sluggish performance when migrating mailboxes to Exchange Online, here are a few of the troubleshooting steps we went through. (The actual was being caused by some barracuda load balancer devices which we had to remove out of the migration path.)

Ensure the Exchange servers are patched with the latest CU

Ensure all flood mitigation, SSL offload, traffic inspection and any IP connection limits are removed from the firewall connections to mail.domain.com (including TMG)

Review Migration endpoint and ensure that MaxConcurrentMigrations are set to a reasonable number for your infrastructure, currently using 35 and 25 MaxConcurrentIncrementalSyncs (use Get-MigrationEndpoint | fl to check.)

Ensure that the correct AV exclusions are in place as per - https://docs.microsoft.com/en-us/exchange/anti-virus-software-in-the-operating-system-on-exchange-servers-exchange-2013-help? (There is a PS script that will generate the correct list of files and locations here - https://docs.microsoft.com/en-us/exchange/anti-virus-software-in-the-operating-system-on-exchange-servers-exchange-2013-help)

#Export all MoveRequest Stats to CSV and review for errors and information alerts or TransientException errors. - Get-MoveRequest | Get-MoveRequestStatistics | Export-CSV Get-MoveRequestStatistics.cs

Test Removing any load balancer devices from the migration path so that only a single CAS server is used.

Check Firewall and CAS server timeouts - https://blogs.technet.microsoft.com/exchangechallengeaccepted/2017/04/15/what-is-keepalivetime-used-for-in-regards-to-exchange/

If you are seeing TransientException or '‘Informational: The request has been paused temporarily because the mailbox is locked. The Microsoft Exchange Mailbox Replication service will attempt to continue processing the request after xx/xx/xxxx’ errors try modifying the MRS timeout values on the Exchange servers. The below config file value should be modified.

(Make a copy of the config file (Take a backup) before modifying the files.)

Find the MRS config file under (Default location) : C:\Program Files\Microsoft\Exchange Server\V15\Bin\MSExchangeMailboxReplication.exe.config

Find the below section in the config file (MrsProxyClientHttpsBinding) and modify the receiveTimeout to 5 minutes from 50 seconds.

Before modification

<binding name="MrsProxyClientHttpsBinding"

receiveTimeout="00:00:50"

sendTimeout="00:00:50">

<reliableSession ordered="true" />

<textMessageEncoding>

<readerQuotas maxArrayLength="1048576"

maxStringContentLength="1048576" />

</textMessageEncoding>

<httpsTransport authenticationScheme="Negotiate"

maxReceivedMessageSize="1048576"

allowCookies="true" />

</binding>

</customBinding>

After modification

<binding name="MrsProxyClientHttpsBinding"

receiveTimeout="00:05:00"