> 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.