Expanding usable capacity on raidz pools by adding devices

[johnkwoods]

We currently have a ZFS pool that has a 6-disk raidz1 vdev. We are running out of space on that zpool, and would like to expand the zpool, to add 2 more identical disks to that volume. Currently, the only known solution would be to backup the filesystems, destroy the zpool, recreate the zpool using 8-disk raidz1, then restore the filesystems.

Other technologies, such as Synology NAS, have a capability of adding a disk to a RAID-5 or RAID-6 storage pool, without having to rebuild it, or even take it offline.

It seems that this could also be done with OpenZFS, perhaps reusing/refactoring code from the sequential reconstruction feature. (I realize it's probably not that simple, or it would be done already..)

Other suggestions that would offer flexibility for raidz users:

• Ability to convert a raidz2 vdev into a raidz1 vdev, increasing the usable storage. (online rebuild)
• Ability to convert a raidz1 vdev into a raidz2 vdev, by adding a device. (online rebuild)

[IvanVolosyuk]

See #12225

[johnkwoods]

Tremendous! Had not seen that the feature had been developed. Thank you!