What causes Boot Device Inaccessible errors on iSCSI disks?

Common causes include missing or outdated iSCSI drivers, corrupted boot configuration data (BCD), failed Windows updates, or incorrect network boot settings. These prevent the server from connecting to the iSCSI target during startup.

How to fix the Boot Device Inaccessible issue?

Microsoft released an update that resolves a known bug affecting servers using iSCSI boot. The fix ensures that drivers and services required for iSCSI initialization load properly during boot, preventing inaccessible disk errors.

How can I fix the Boot Device Inaccessible error manually?

To fix the error, you can update iSCSI drivers, rebuild the boot configuration data (BCD), check storage network connectivity, and apply Microsoft’s latest patch. In some cases, rolling back a recent faulty update may also resolve the problem.

Does this error affect only Windows Server with iSCSI?

The issue is most common on Windows Server systems that boot from iSCSI disks, but similar Boot Device Inaccessible errors can also occur on local disks if critical drivers or boot files are missing.

Fix: Boot Device Inaccessible Error on Windows Server 2025 with iSCSI

How to Fix Windows Server 2025 Boot Error: “Boot Device Inaccessible” on iSCSI Disks.

Microsoft released a patch to fix the “boot device inaccessible” error on Windows Servers booting from iSCSI disks. This article explains the issue, its causes, and provides a step-by-step guide to apply the fix safely.

Quick Summary

Many organizations running Windows Server 2025 on iSCSI-based boot systems encountered the “boot device inaccessible” error.
Microsoft recognized this as a known bug that stopped servers from booting properly after updates. The issue is now fixed with patch KB5051987. This article explains the root cause, the official fix, and offers a step-by-step troubleshooting guide to help you apply the patch or recover if your server is affected.

What is “Boot Device Inaccessible” Error?

The “Boot Device Inaccessible” error in Windows Server occurs when the system cannot access the disk that holds the operating system. In iSCSI environments, this often happens due to driver issues, incorrect boot configuration, or failed updates, preventing the server from booting properly.

When Windows fails to access the system boot volume during startup, it shows the0x0000007B – INACCESSIBLE_BOOT_DEVICE error on Windows Server 2025.

Many peoples have noted this issue mainly on systems set up to boot from iSCSI targets.

Rather than finishing the boot process, the server would restart or show a blue screen. This disrupts important business workloads.

Why Did It Happen on Windows Server 2025?

Changes in how Windows Server 2025 handles iSCSI boot initialization.
Incompatibility between certain updates and iSCSI drivers.
Network dependency during boot not being properly recognized.

Essentially, the OS was unable to establish a stable connection to the iSCSI target during boot, leading to the inaccessible device error.

Official Fix

Microsoft released KB5051987 in August 2025 as part of the cumulative updates. This update resolves the issue by:

Correcting the initialization sequence for iSCSI boot systems.
Ensuring network paths are available before disk access.
Improving error handling for iSCSI drivers during startup.

Microsoft originally released KB5051987 on February 11, 2025, which was Patch Tuesday. In August 2025, Microsoft updated its Windows release health dashboard. This update also fixes the ‘boot device inaccessible’ error for servers using iSCSI.

If your environment uses iSCSI boot with Windows Server 2025, applying this update is strongly recommended.
Without it, you may face repeat crashes after patching or rebooting.

Step-by-Step: How to Apply the Fix

Step 1: Verify the Problem

Confirm that your server is actually failing with INACCESSIBLE_BOOT_DEVICE.
Usually, the error happens immediately after the Windows logo appears during boot.

Step 2: Boot into Recovery Mode

Insert the Windows Server 2025 installation media (ISO or DVD).
Boot from the media and select Repair your computer.
Navigate to Troubleshoot → Advanced Options → Command Prompt.

Step 3: Check Network & iSCSI Connectivity

From recovery, verify that your NICs are detected and iSCSI connection can be established:

iscsicli ListTargets

Step 4: Roll Back the Faulty Update (If Necessary)

If you’re unable to boot, remove the problematic update:

dism /image:C:\ /get-packages
dism /image:C:\ /remove-package /packagename:Package_for_KBxxxxxx~...

Step 5: Install KB5051987

Once stable, install the fixed update:

wusa.exe Windows10.0-KB5051987-x64.msu /quiet /norestart

Alternatively, use Windows Update or WSUS to push the patch across servers.

Step 6: Reboot and Validate

Restart your server.
Confirm that it boots successfully into Windows Server 2025.
Check Event Viewer for any iSCSI or boot errors.

Best Practices for Avoiding iSCSI Boot Issues

Always validate updates in a test environment before applying to production.
Maintain offline backups or snapshots of boot volumes.
Use redundant iSCSI targets and network paths for resilience.
Monitor the Windows Release Health dashboard for known issues.

FAQs

1. What causes the “boot device inaccessible” error in Windows Server 2025?

It’s caused by the OS being unable to access the boot volume during startup, particularly in iSCSI boot environments due to
a driver/initialization bug.

2. How do I know if I’m affected?

If your server boots via iSCSI and started showing 0x0000007B errors after updates, you are likely affected.

3. Which update fixes the problem?

The issue is resolved in KB5051987, released in August 2025 cumulative updates for Windows Server 2025.

4. Can I prevent this before updating?

Yes, by snapshotting or backing up your server before installing patches and ensuring you test updates in a staging environment.

5. Do I need to reconfigure iSCSI after applying the fix?

No, the patch modifies how Windows initializes drivers, so no configuration changes are required in most environments.

Conclusion

The “boot device inaccessible” error on Windows Server 2025 with iSCSI boot systems created significant issues for server admins.

Microsoft has provided a permanent solution through KB5051987. By applying this update and following best practices, you can maintain stable and secure servers.

If you relies on iSCSI boot configurations, patch early and monitor updates closely to prevent downtime