more warnings

howto/lvm.md

@@ -159,6 +159,11 @@ should do the following:
 
 # Shrinking
 
+Shrinking the filesystem is also possible, but is more risky. It is
+very important to reduce the size of the filesystem *before* resizing
+the size of the logical volume, so the order of the steps below is
+critical.
+
  1. unmount the filesystem:
  
         umount /mnt
@@ -185,7 +190,9 @@ should do the following:
         lvreduce -L -5G vg/mnt
 
     WARNING: make sure the resulting size matches exactly the one
-    specified in the `resize2fs` command above.
+    specified in the `resize2fs` command above. For more precision,
+    `resize2fs` and `lvreduce` can both accept an argument (`s`) in
+    "sectors" (512 bytes).
 
  5. tell ext to resize the filesystem *again*: