Recently I was working on System Center 2016 Data Protection Manager (DPM) that has some free space problems on the Modern Backup Storage (MBS) volume in Windows Server 2016.
The DPM Server is deployed in a VM and I am leveraging Data Deduplication.
Check the following article to learn more on how to reduce DPM 2016 storage by enabling deduplication on Modern Backup Storage.
I extended the Virtual Disk by adding 6TB to the DPM Storage Pool, and then I extended the Disk size in Disk Management. All without any problems. But when I was checking the disk size in Windows Explorer the size was reported incorrectly. The old size was still showing 24TB.

If we look at the Virtual Disk under Storage Pools, we can see the actual size is 30TB.

And in Disk Management, the E Volume is also reporting 30TB.

All DPM backup jobs start failing… This is not good!!!
Fortunately, the fix is simple…
- Open an elevated command prompt (cmd) window and type: DISKPART
- Next, you need to list all volumes by typing: List Volume
- You need to select the volume that has the wrong file system size, type: Select Volume E
- In my case, E is the letter of the affected volume.
- Finally, you need to extend the volume by typing: Extend FileSystem

Go to Windows Explorer again and check the volume size. The correct disk size is showing now.

That’s it!
Cheers,
-Ch@rbel-