I have a Time Machine backup, and have bought an identical external drive, with the intention of running TM on both drives.
I know that I can just plug the new drive in and configure it as a TM target, but I have a significant amount of history in the backup that is no longer on the source system (due to disk space constraints). I'd like to start the redundant backup as a mirror of the original, so that the older weekly data is available from either TM. Ultimately, one of the disks will be at the office, the other at home. Anything else isn't really a satisfactory DR solution.
I've found any number of discussions about cloning TMs and moving TM from one disk to another, but not an answer to this question. Perhaps it's perfectly straightforward and I'm over-thinking it. But I don't want to have these disks chugging for hours copying data that isn't going to produce a second functional TM.
Thanks in advance.