diff --git a/Ubuntu-18.04-Root-on-ZFS.md b/Ubuntu-18.04-Root-on-ZFS.md
index c71c21c..9b7c52e 100644
--- a/Ubuntu-18.04-Root-on-ZFS.md
+++ b/Ubuntu-18.04-Root-on-ZFS.md
@@ -5,6 +5,7 @@
 
 ### System Requirements
 * [Ubuntu 18.04.1 ("Bionic") Desktop CD](http://releases.ubuntu.com/18.04/ubuntu-18.04.1-desktop-amd64.iso) (*not* any server images)
+* A drive which presents 512B logical sectors.  Installing on a drive which presents 4KiB logical sectors (a “4Kn” drive) should work with UEFI partitioning, but this has not been tested.
 
 Computers that have less than 2 GiB of memory run ZFS slowly.  4 GiB of memory is recommended for normal performance in basic workloads.  If you wish to use deduplication, you will need [massive amounts of RAM](http://wiki.freebsd.org/ZFSTuningGuide#Deduplication). Enabling deduplication is a permanent change that cannot be easily reverted.