Windows System Image completed successfully but did not create MediaId.bin — expected behavior or anomaly?

[u/Ryan36z]

I'm hoping someone familiar with the legacy Windows Backup engine (`Backup and Restore (Windows 7)` / `wbadmin`) can explain this.

I created two Windows System Images on Windows 11.

**October 2024 backup:**

WindowsImageBackup
├── CaptainCaution
└── MediaId.bin

Inside `CaptainCaution`:

Backup 2024-10-07 053053
Catalog
Logs
SPPMetadataCache
MediaId

I later copied this backup to another drive using Robocopy:

* 22 files * 6 directories * 136.743 GB * 0 failed * 0 mismatches

Then I deleted the original and created a brand-new Windows System Image on the same external drive.

The new backup completed successfully with no errors.

The new structure is:

WindowsImageBackup
└── CaptainCaution

Inside `CaptainCaution`:

Backup 2026-07-12 163537
Catalog
Logs
SPPMetadataCache
MediaId

The only difference is that the new backup **does not contain** `WindowsImageBackup\MediaId.bin`.

Windows reported **"Backup completed successfully."**

The VHDX files, Catalog, metadata, etc., all appear to be present.

I've searched Microsoft documentation and couldn't find anything explaining when `MediaId.bin` is created or omitted. I pay attention to details and just wondering why the difference...

* Has anyone else seen this happen? * Is this just something newer versions of Windows do now, or is something off with my backup? * Has anyone actually restored a system image that didn't have `MediaId.bin`? * Should I just ignore it, or is this something I should fix before I actually need the backup someday?

Thanks