My Azure service depends on a huge filetree and I try to deal with that filetree using VHDs. What I currently plan to do is create a VHD file, mount it, format it to NTFS and enable NTFS transparent compression, then copy the filetree there. Then I'll upload the VHD file to Windows Azure Blob Storage. When an Azure instance starts it will download the VHD file, mount it and use it transparently as if it was in a local folder.

Everything sounds great, but the filetree is something like 800 megabytes. With NTFS compression enabled it fits into a 600 megabytes VHD file. Yet if I ZIP the filetree it occupies around 400 megabytes.

I want to have a file as small as possible and without a need to unpack it - so that it can be "mounted" and used transparently. That's like VHD, but with better compression.

Can I have a VHD with better compression?

  • Sounds like you want/need some form of native compression for VHDs, only with better compression? That's not really so much... well, it's a self-contradictory requirement (if I'm reading it right). What you get is what you get in native compression, but check Brent's answer on how to squeeze smaller file sizes out of your existing VHDs, which is the only thing I can think of that may help you. Aug 1, 2012 at 16:58
  • @HopelessN00b VHDs have native compression? Can you tell more about that? May 11, 2015 at 15:34
  • I use a VHD file with VirtualPC and I enabled NTFS file compression on it. It saves about 30% of the size. Not sure if this is an option on Azure. At least for the upload you will have to transfer it uncompressed (or ZIP it, upload, then unzip on the cloud). May 15, 2015 at 22:53
  • As an alternative, you can store the files in a ZIP file, and mount that. There are (were?) tools that can mount a ZIP file. Even Windows tries to show the content of ZIP files as if they were regular folders, but the mount tools actually make it a "real" filesystem (so they really mount it, not just a GUI hack like Windows Explorer). Jan 12, 2022 at 10:33

2 Answers 2


VHDs are already fairly well shrunk however, just like any normal hard drive they can fragment and depending on the type of VHD may need to be shrunk periodically to keep them smaller. You could try to shrink the VHD before uploading it to see if that improves it at all or not.


  • If he creates a new ("empty") VHD and fills it with files, then it is already more or less optimally shrunk. May 12, 2015 at 14:05

Seems that the guy in the link below managed to compress a bunch of large VMs with over 180 GB size into a VHDX drive with only 25 GB size !

Main technique as far as I have followed is activating socalled deduplication in the VHDX drive (works on servers and can be made to work with Win 8.1 and above) and then defragmenting and compacting the virtual disk as by standard.

I would be quite surprised if defragmenting really would have an effect on size here, but this is just what he has done.

Further packing with 7zip allowed even a compression down to 16 GB but with loosing the flexibility of a virtual disk.


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