It mirrors in the sense that the end result will be the same.   This is for v6.9.x, while it should also work with v6.10.x I didn't test it, and don't like to assume.   You need to have both the old and new replacement devices connected at the same time, if you can have all 4 you can do both replacements and then reset cache config, if not do one, reset cache config, do the other reset cache config again.   First you need to partition the new device, to do that form