As I wrote on 18 March:

1. Time Machine can share a partition with other data. The bad news is that it will expand to fill all of the free space on the partition it is on, so your free space for the other data will gradually disappear.

Options are to repartition it non-destructively as discussed, or to create a disk image on the disk that will not expand beyond its defined size.

Of course!

I tried to partition the old ext drive (hence the faffing) but it wouldn't let me, I guess because (at a guess) it was too fragmented - the old "Not enough Free space" error. Know a good free defragger?

In reply to a post by ian_c:

Of course!

Know a good free defragger?

Most of them seem to be paid apps like TechTool. There's a free version of one, but it's limited to 100MB partitions, I believe. Simplest I've seen is to Carbon Copy Clone the partition to another location, reformat, then CCC it back again. But that isn't really what you're looking for.

Ah well.

The only files on te disk are my totallylegitimatedownloads. If I lose them it is a pain, but no great tragedy.