What's faster, cp -R or unpacking tar.gz files?

Buttle Butkus asked:

I have some tar.gz files that total many gigabytes on a CentOS system. Most of the tar.gz files are actually pretty small, but the ones with images are large. One is 7.7G, another is about 4G, and a couple around 1G.

I have unpacked the files once already and now I want a second copy of all those files.

I assumed that copying the unpacked files would be faster than re-unpacking them. But I started running cp -R about 10 minutes ago and so far less than 500M is copied. I feel certain that the unpacking process was faster.

Am I right?

And if so, why? It doesn’t seem to make sense that unpacking would be faster than simply duplicating existing structures.

My answer:

Reading a very small file is much faster than reading a bunch of large files. This is generally true even if the CPU has to decompress it.

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