Thanks

I plugged the second drive into the same SATA cable/power and successfully wrote 2TB to it, so I guess I'll be returning the first drive. I still need to test the third one.

At this point in the process I'm wishing I'd used FreeNAS for my ZFS array rather than Ubuntu. The ten step process to replace each drive is a little tedious and error prone (I've already accidentally over written a partition table on one disk).

It would be a great deal easier if I wasn't being a cheapskate and not using the same 3 drives I'm mirroring under ZFS to also boot Ubuntu using a standard Linux mirrored array.

- add new drive
- copy partition table from existing drive
- randomise guid partition labels on new drive
- resize the ZFS partition on the new drive from ~2TB to ~4TB
- dd the boot partition over from old drive
- fail and remove the old drive from the Linux RAID mirror
- add the new drive to the Linux RAID mirror
- replace the old drive with the new drive in the ZFS mirror
- run grub install
- wait 10+ hours for the Linux mirror and ZFS to rebuild

Repeat three times and hope at the end of it all that ZFS correctly expands into the new space...