> Though I'd really need 2 drives - one replacement, and a mirror.

Yea, with just a single drive it's not really a backup is it?

> If I copy some files with zfs to another drive, I'd also like to check that there wasn't an error in the copying process.

That's what rsync is for.

> I wouldn't mind buying a mirror set a year or two ago, but storage is so expensive now.

Prices went up, yes but not that much to be fair. And I think it mostly affected M2 disks.

Here's my very limited notes on HDD prices.

In 21 october 2023, a 22 TB disk cost me 0.37 SEK per gigabyte.

In 28 may 2026, a 26 TB disk cost me 0.36 SEK per gigabyte.

Both were WD red disks.

> In 28 may 2026, a 26 TB disk cost me 0.36 SEK per gigabyte.

The best price I can find for a 24gb+ hard drive is $1250 AUD for a 24gb Seagate Barracuda drive, at my local computer store. They're a similar price on amazon. Amazon US has refurbed drives too, which are a little cheaper but not much.

$1250 for 24gb is $52AUD per gigabyte, or 353 Swedish Krona per gigabyte.