diff --git a/ZFS/The 80% rule.md b/ZFS/The 80% rule.md
index 8b13789..d5832c6 100644
--- a/ZFS/The 80% rule.md	
+++ b/ZFS/The 80% rule.md	
@@ -1 +1,7 @@
+I don't know where this rule came from, but is bad and imprecise. 
 
+For HDD and blockstorage, performance will suffer if you fill your pool above 50%.  
+
+For SSDs and blockstorage, fragmentation will not hinder performance that much, since there are no heads involved. Maybe you have some pseudo SLC cache that will suffer.
+
+For HDD/SSD and datasets, there is no reason why you should not be able to fill up your 80TB pool with 79TB of data.