Can cat be used to clone a partition?

Question

For example, can I do:

cat /dev/sda1 > /dev/sda2

instead of using dd, and if not, why will this not work?

Answer 1

In principle, you could use either. There are few important differences, but none that apply here.

• When you use > redirection, the target file is opened, and truncated. Only then it is written to. However this does not apply to block devices — they have a fixed size, so “truncation” doesn't do anything to them.

• With cat you can not easily tell it to only copy the first n bytes or skip/seek. This is what dd is useful for.

• cat does not let you specify a block size. This won't matter today when block sizes are masked by the file systems being used, but it used to make a difference where devices would be read from with specific block sizes (tapes).

• For hard disks, cat may be slightly faster (better even than dd with a well-chosen block size, let alone the default which slows things down).