When not to use NTFS Compression

When NTFS compression is not a so brilliant idea.                                                                                   

I was running low on disk space, and I had virtual machines that took up large disk space while they are actually sparse inside. So, I decided to compress them. It worked great, their disk space was reduced significantly. But when I tried to use one of the virtual machines, it was painfully slow. Things that should take a few seconds took multiple minutes. The slightest disk changes took enormous amounts of time, and the CPU usage went crazy high. I couldn’t bear it for a long time, and I had nothing but the compression to blame. I uncompressed the machine and tried using it again and it worked extremely well!

It turns out that NTFS compression is not a very good idea for huge files that you plan to modify. I think things would have been just fine if the files were read only. So, the next time you consider compressing your file-system, do it on a per folder/file basis.

Edit:

It seems like this issue is not that severe on Windows 10. The same compressed virtual machine works pretty smoothly when run on Windows 10, but painfully slow on Ubuntu. Maybe it’s the open-source NTFS implementation that’s to be blamed?

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