why second time cp command is faster

Question

When I execute cp folder1 folder2 -rf,for the first time it takes around 10 mins. But when it I execute the second command cp folder1 folder3 -rf, it takes around 1 min. folder1 contains about 100 000 files.

Why is there run time improvement for the second time?

Answer 1

This is because of page caching. Run sync ; echo 3 > /proc/sys/vm/drop_caches to make it slow again.

Further reading:

• http://jim.studt.net/depository/index.php/flushing-caches-for-benchmarking-in-linux
• https://superuser.com/a/319287/236874