Not currently. The "block pointer rewrite" feature is what's needed for this (online defragmenting) and a host of other features (migrating between vdev types, removing vdevs from the pool, etc).
It's under development and people are actively working on it, but it's not yet available as part of any ZFS release.
It's under development and people are actively working on it, but it's not yet available as part of any ZFS release.