It seems like just using a sparse file would make things simpler. I guess there would be potential inefficiency when you try to move the VM to another drive, but for just storing and using the VM in place it doesn't seem like this has to be hard: a TRIM inside the VM gets translated into a hole punch in the disk image file, which gets translated into a TRIM sent to the underlying storage.

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bayindirh 3 days ago | parent | next [-]

rsync in Linux can move sparse files as efficiently as possible, but I don't know if there's an equivalent in Windows.

It'd be very strange if there is not.

	▲	mjmas 3 days ago \| parent [-]
		as far as i know robocopy should

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Dylan16807 3 days ago | parent | prev [-]

Sparse files would be useful but I'm pretty sure sparse files on NTFS always reserve their full size. Eating 1TB of free space for my ext4.vhdx is a non-starter.

	▲	banana_giraffe 3 days ago \| parent \| next [-]
		https://gist.github.com/Q726kbXuN/c80028aa1714032546d3b442c1... Nope, they don't eat up space. One of the fun side effects of sparse files on NTFS is calling WriteFile on the sparse file can lead to an ERROR_DISK_QUOTA_EXCEEDED error, which applications tend to not expect.
	▲	wtallis 3 days ago \| parent \| prev [-]
		Based on https://learn.microsoft.com/en-us/windows/win32/fileio/spars... and subsequent links, it sounds like sparse files count against disk quotas as if they weren't sparse, but otherwise sparse files actually work on NTFS. If sparse files didn't save on actual space allocations, it would simply be a lie to call them sparse files. Granted, that's totally something Microsoft would do, and has done for other features they lack, but that doesn't seem to be the case here.