Damn

So I install the new 4-drive hotswap bay into my PC. Except I didn't realise that my motherboard only has 5 SATA slots; I'm using 2 for the internal root+mirror. Ugh. So I plug in an old SiI 3512 card (1.5Gb/s) and move the mirror disk onto that (it's an old Samsung 500Gb drive; it may only be 1.5Gb/s anyway!).

Hardware fiddle hardware fiddle hardware fiddle. It's not easy to install this bay!

OK, done.

Power up... wait for fsck (192 days since last check).

We're back.

Without a root mirror. WTF?

This isn't good. It's not finding the disk! If I unplug it and plug it into an internal SATA port it's still not found, which either means hotplug isn't supported on the internal ports or the drive has stopped responding (or the cable is bad?).

This is ANNOYING.

Hrmmph

So turns out the motherboard wasn't set to AHCI, which is why hotswap wasn't working. Fixed that, rebooted, and now the disk is seen. Let's resync those mirrors!

I wonder why this SiI card wasn't detecting the disk. The card, itself, was detected and the sata-sil driver loaded. But no disk showed up. Hmm.

(Not sure if I've ever used this card under CentOS 6 or if it was CentOS 5. Pretty sure it was a different motherboard).

This 'cheap' solution could turn out to be expensive!