I was referring to this sequence of events: 1) 2-way mirroring across 2 drives 2) one drive fails 3) buy and plug a new drive 4) rebalance to have 3-way mirroring across 3 drives (with one being out): this is currently not possible 5) remove the failed drive, ending with 2-way mirroring across 2 drives
But it seems that you are referring to: 1) 2-way mirroring across 3 drives 2) one drive fails 3) rebalance to have 2-way mirroring across the 2 working drives 4) remove the failed drive, ending with 2-way mirroring across 2 drives
I assume that people don't/won't start the initial RAID1 with 3 drives.
Anyway, I would find 3-way mirroring across 3 drives very useful as it gives a simple identical foolproof process to replace a faulty hard drive, whether it has just a few corrupted data (but still readable) or have completely failed : just plug a new drive, rebalance, reboot and remove the defective drive.