diff --git a/docs/Getting Started/Debian/Debian Buster Root on ZFS.rst b/docs/Getting Started/Debian/Debian Buster Root on ZFS.rst
index 7915682..5d91124 100644
--- a/docs/Getting Started/Debian/Debian Buster Root on ZFS.rst	
+++ b/docs/Getting Started/Debian/Debian Buster Root on ZFS.rst	
@@ -167,15 +167,28 @@ Step 2: Disk Formatting
 
 #. If you are re-using a disk, clear it as necessary:
 
-   If the disk was previously used in an MD array, zero the superblock::
+   If the disk was previously used in an MD array::
 
      apt install --yes mdadm
+
+     # See if one or more MD arrays are active:
+     cat /proc/mdstat
+     # If so, stop them (replace ``md0`` as required):
+     mdadm --stop /dev/md0
+
+     # For an array using the whole disk:
      mdadm --zero-superblock --force $DISK
+     # For an array using a partition:
+     mdadm --zero-superblock --force ${DISK}-part2
 
    Clear the partition table::
 
      sgdisk --zap-all $DISK
 
+   If you get a message about the kernel still using the old partition table,
+   reboot and start over (except that you can skip this step).
+
+
 #. Partition your disk(s):
 
    Run this if you need legacy (BIOS) booting::
diff --git a/docs/Getting Started/Ubuntu/Ubuntu 20.04 Root on ZFS.rst b/docs/Getting Started/Ubuntu/Ubuntu 20.04 Root on ZFS.rst
index c384322..737e94c 100644
--- a/docs/Getting Started/Ubuntu/Ubuntu 20.04 Root on ZFS.rst	
+++ b/docs/Getting Started/Ubuntu/Ubuntu 20.04 Root on ZFS.rst	
@@ -197,15 +197,27 @@ Step 2: Disk Formatting
 
 #. If you are re-using a disk, clear it as necessary:
 
-   If the disk was previously used in an MD array, zero the superblock::
+   If the disk was previously used in an MD array::
 
      apt install --yes mdadm
+
+     # See if one or more MD arrays are active:
+     cat /proc/mdstat
+     # If so, stop them (replace ``md0`` as required):
+     mdadm --stop /dev/md0
+
+     # For an array using the whole disk:
      mdadm --zero-superblock --force $DISK
+     # For an array using a partition (e.g. a swap partition per this HOWTO):
+     mdadm --zero-superblock --force ${DISK}-part2
 
    Clear the partition table::
 
      sgdisk --zap-all $DISK
 
+   If you get a message about the kernel still using the old partition table,
+   reboot and start over (except that you can skip this step).
+
 #. Create bootloader partition(s)::
 
      sgdisk     -n1:1M:+512M   -t1:EF00 $DISK