iMac 21.5 Core i3 mid 2010 SSD swap, is a bay required When swapping out the mechanical drive for an SSD in these machines, I've seen people put in a size-up caddy.  But is this needed - can I just gaffa tape the drive to the back or something?
If it never gets moved around, you could actually just leave it loose inside the casing.

It won't make any practical difference, you just don't want to be shaking it around unnecessarily.
I wouldn't think of doing it in a laptop, but a desktop it will be fine.

I had an SSD hanging loose inside the optical bay of a Mac Pro for about 5 years with no ill-effects at all - &amp; in fact I'm not sure that more than one of the Mac Pros here has a proper mount at all, &amp; that one is only because the machine came with it. As soon as I need the bay for another big HD, it will go up in the optical bay like the rest.