> If you're using RAID1 vdevs, you could always remove and add mirrors.
This is still answering the wrong question, unless by "add mirrors" you mean "add another drive to a mirrored vdev and get more usable capacity", which I don't think is how ZFS works and would be strange to summarize as "add mirrors".
I'm trying to discuss an idea you don't seem to have any terminology for. Can you please try to meet me halfway and at least respond in a manner that makes it clear you understand there's a real distinction to be made?
You can add and removes devs from a vdev in ZFS now, with this feature, giving you the ability to resize a vdev. But only upwards. Downwards isn't possible yet.
This is still answering the wrong question, unless by "add mirrors" you mean "add another drive to a mirrored vdev and get more usable capacity", which I don't think is how ZFS works and would be strange to summarize as "add mirrors".
I'm trying to discuss an idea you don't seem to have any terminology for. Can you please try to meet me halfway and at least respond in a manner that makes it clear you understand there's a real distinction to be made?