It's good to see that they were pretty conservative about the expansion.
Not only is expansion completely transparent and resumable, it also maintains redundancy throughout the process.
That said, there is one tiny caveat people should be aware of:
> After the expansion completes, old blocks remain with their old data-to-parity ratio (e.g. 5-wide RAIDZ2, has 3 data to 2 parity), but distributed among the larger set of disks. New blocks will be written with the new data-to-parity
ratio (e.g. a 5-wide RAIDZ2 which has been expanded once to 6-wide, has 4 data to 2 parity).
Not only is expansion completely transparent and resumable, it also maintains redundancy throughout the process.
That said, there is one tiny caveat people should be aware of:
> After the expansion completes, old blocks remain with their old data-to-parity ratio (e.g. 5-wide RAIDZ2, has 3 data to 2 parity), but distributed among the larger set of disks. New blocks will be written with the new data-to-parity ratio (e.g. a 5-wide RAIDZ2 which has been expanded once to 6-wide, has 4 data to 2 parity).