adding drive to raidz1

[Randy Bush]

> 2) Replace each (and every) disk in your raidz pool one by one,
> letting it resilver after inserting each upgraded disk

ok.  given

    # zpool status
      pool: tank
     state: ONLINE
     scrub: none requested
    config:

	    NAME        STATE     READ WRITE CKSUM
	    tank        ONLINE       0     0     0
	      raidz1    ONLINE       0     0     0
		ad4s3   ONLINE       0     0     0
		ad5s3   ONLINE       0     0     0
		ad6s1   ONLINE       0     0     0
	      ad7s1     ONLINE       0     0     0

how do i get ad7s1 offline?  i can't detach it.  will using it in a
replace do the trick?

and then how do i replace the four slices one by one?

sorry, but this is a distant system and after screwing up once, i am a
bit cautious.

just