Fix Mailbox Export Stalled Due to Source Disk Latency

Are you struggling with an Exchange Server where the mailbox export stalled due to source disk latency? Or see a StalledDueToTarget_DiskLatency alert popup on the diagnosis report. This is not a new scenario but a common occurrence that many novice admins conducting their first on-premise-inter-domain or on-premise-to-cloud migration have encountered before.

So in order to fix this error we have put together a list of solutions that can help you get out of this quagmire and complete the migration easily. Before we begin listing the solutions let us go through the possible reasons why the error occurs.

What Causes Mailbox Export Stalled Due to Source Disk Latency?

Ideally, migrations should be conducted in a digitally sanitized environment where no other unrelated resource-heavy task is running. However, it is not possible to construct such conditions. This means many times migrations and the secondary task are in a tug of war, examples and explanations of which are given below.

Also Read: How to Fix StalledDuetoMRS_Quarantined Error in Exchange Migrations

High Disk I/O:

• The migration agents try to over-extend the reading of data at the source database and end up accumulating redundant data.
• There might be too many ongoing heavy disk load operations like backups which cause latency.

Inefficient Migration Batches:

• To speed up the process, admins may try to add a large number of mailboxes in a single migration batch. However, this may have the opposite effect, as the server may get stuck while moving these many mailboxes together.
• An equally likely situation that causes a mailbox export to stall due to source disk latency is the Exchange’s WLM under go throttle. This is due to self-induced source disk stress.

Hardware/Configuration Issues:

• Older/suboptimal storage (non-SSD, bad RAID, failing disks) worsens latency.
• Exchange’s dependence on disk I/O amplifies these hardware inefficiencies during migration.

Migration-Specific Factors where you might see a StalledDueToTarget_DiskLatency:

• Simultaneous read (source) and write (target) operations increase load.
• Stresses source disk further if not optimized and or has network storage delays.

How to Fix Mailbox Export Stalled Due to Source Disk Latency Errors?

Windows Machines (both Desktop and Server variants) contain a Performance Monitoring kit.

Admin can deploy it by tapping the Windows + R keys together and typing a PerfMon.

Use it at the end point where the error occurs that is
On the source side if you see the StalledDueToSource_DiskLatency and destination if StalledDueToTarget_DiskLatency. Monitor the different metrics like Disk Queue Length, Average Disk sec/Read, etc, and determine where and when exactly the bottleneck occurs in the migration.

Also Read: Resolve Stalled Due to Target Processor Error in Exchange Server Migrations

Apart from the software-level checks, see if your hardware is up to the task. Older disks are more prone to throwing in StalledDueToTarget_DiskLatency or StalledDueToTarget_DiskLatency. So, if your budget allows, consider upgrading to faster, server-grade disks (or SSDs). While you are at it, make sure RAID controllers and drivers are up to date.

• Step 1: If a migration request is stuck, use PowerShell to remove it:

Remove-MoveRequest –Identity "mailbox@domain.com"

• Step 2: Then, reissue the move (with increased priority) :

New-MoveRequest –Identity "mailbox@domain.com" –BatchName "MigrationBatch" –Priority Highest

This helps clear any lingering requests that might be adding to the disk load.

• Step 3: Suspend and Resume:

For particularly large move batches, consider suspending and then resuming the requests to give the disk subsystem a chance to recover:

Suspend-MoveRequest -Identity "mailbox@domain.com"
# Wait 10–20 minutes
Resume-MoveRequest -Identity "mailbox@domain.com"

This method can effectively manage temporary spikes in disk latency.

Advance Tip: Schedule Migrations During Off-Hours or When User load is at a minimum:

Migration is a resource-intensive task where so schedule it when demand from other sources is at its minimum to avoid I/O contention.

Admins may try to readjust WLM limits. This comes under advanced practices and should only be considered as a last resort. There is a way by which adjusting the Exchange Workload Management (WLM) can expand the maximum concurrent moves without overwhelming the disk. However, it can affect other components of the server so exercise caution.

How is a Disk Latency type of Stall Different from Other Stall Error Types?

Here is a condensed generalized table describing the difference between the Disk Latency and Other types of Stall.

Criteria	Disk Latency Stall	Other Stall Errors
Severity	High – indicates hardware/I/O bottleneck.	Moderate – often due to transient throttling or delays.
Frequency	Less frequent in optimized environments.	Common in large-scale or high-load migrations.
Cause	Poor disk performance (high I/O, aging hardware).	Throttling, temporary replication, or availability delays.
Impact	Stalls move requests; extends migration time.	Queues mailboxes; slow migration without halting progress.
Resolution	Requires hardware upgrades or reconfiguration.	Adjusting batch sizes or throttling settings usually suffices.

Alternative Migration Mechanism for Faster and Error-Free Transfer

SysTools Exchange Server to Office 365 migration tool can make complex inter-platform migration extremely easy. You can also get its sister tool focused on Exchange on-premise to Exchange on-premise type inter-domain transfers.

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By breaking down the manual script-based transfer into different sections and elevating the entire process into a neatly packaged GUI system it helps admins conduct the transfer in record time.

The tool comes with a built-in concurrency slider mechanism. With its help, the admin can control how many users should be shifted together. By keeping the slider at its lowermost limit the admin can perform the task in a manner that does not overwhelm their system. Thus avoid the stalled due to source/target disk latency error entirely. Given below are the set of steps you can use to run the tool.

Step 1. Download the tool install and launch it. Use the main screen to select the desired Endpoints. In the workload area mark the boxes next to the emails and apply a date filter if need be.

Step 2. To fix mailbox export stalled due to source disk latency fill in all the accurate information in the Source validation screen, Validate it, and press Next.

Step 3. Likewise, replicate the validation process for the target as well i.e. fill validate and hit Next.

Step 4. Use any one of three mapping options (Fetch, Import, or Download) to complete the user data entry in the tool.

Step 5. Preview the data, select the accounts you want to migrate, prioritize the most critical accounts, validate, and hit start.

Conclusion

So now the mailbox export stalled due to source disk latency or target disk latency is no longer a hurdle for admins conducting Exchange Database migrations.

In this write, we gave a full list of scenario-wise diagnostic tests and their exact remedy. Moreover, as an alternative to the regular migration process, the admins can use the recommended tool prescribed earlier in the blog.

Frequently Asked Questions on StalledDueToTarget_DiskLatency Error

• Q: Can we predict whether or not an Exchange Server will undergo a disk latency error?
  A: Yes, if you are vigilant you can identify hidden telltale signs. These usually occur in the form of slow app performance, and longer response times for typical requests like file access, etc. All such symptoms indicate that there is something wrong with the Exchange Server and there are high chance that it will throw in a StalledDueTo DiskLatency error.
• Q: Is network level latency in any way responsible for StalledDueToTarget_DiskLatency errors?
  A: The disk and network are two separate components that work largely independently of each other. However, a slow network can exacerbate the problem as now the information delivery is slow and it takes more time to write the data in the target server. Not only that, but admins might see that the source disk is under more stress which evolves into stalls.
• Q: There are a lot of details in the Performance Monitor utility, which metric gives me the best diagnosis during the StalledDueToSource_DiskLatency troubleshooting?
  A: Focus on “PhysicalDisk()% Disk Time”, “PhysicalDisk()\Avg. Disk Queue Length”, and “PhysicalDisk(*)\Avg. Disk sec/Read”. These counters provide insight into disk utilization, queue depth, and read latency, respectively. They can help you to figure out where exactly the CPU/memory bottleneck lies.
• Q: What are the potential risks of adjusting WLM limits, and how can I mitigate them?
  A: If you don’t increase the WLM limits enough you won’t see any change and the error continues, at the same time increasing it too much can overwhelm the server, leading to performance issues or even crashes.
  So the best way forward is to make incremental adjustments instead of large changes, while you are doing this monitor server performance closely. You should be ready to revert any and all changes if necessary.