> Can Windows really let you shrink NTFS while mounted?
Yes, I have done it, even on the running system partition, and no reboot required. Just right click the partition in Disk Management and select Shrink. It will calculate the smallest size the partition can shrink to, and you can use that or any larger size.
That will happen when there are unmovable files. There are a few tricks you can do to unlock some of these files, or you can use an external utility that you reboot into.
This article is from a vendor of such a utility, but it also describes how to unlock some of the unmovable files within Windows:
Yes, I have done it, even on the running system partition, and no reboot required. Just right click the partition in Disk Management and select Shrink. It will calculate the smallest size the partition can shrink to, and you can use that or any larger size.