"I thought RAID and SSD were a terrible combination. As if both drives do exactly the same writes at the same time, chances are they will fail at the same time."

This is a very good thought and you should be thinking it.

However, it is really only applicable to raid mirrors. Raid stripes will not have identical wear lifespans.

All of our mirrored boot devices are either:

- current intel enterprise SSD paired with the previous generation intel enterprise SSD

or:

- current intel enterprise SSD paired with current samsung enterprise SSD

That way if there is a usage related failure (or some weird firmware bug triggered by use pattern) they don't seize up identically.