Fixed <dst_dev> size requirements.

 - As bugreported by: Jeff

diff --git a/README b/README
index b02fc61..87a3a1d 100644 (file)
--- a/README
+++ b/README
@@ -56,10 +56,15 @@ Possible device cases (watch out for <src_dev> vs. <dst_dev> differences!):
                drive in the system with the exactly same partition size is
                recommended
 
-       <dst_dev> is a file: File must exist but it will be enlarged when
-               needed. Commands:
-                       rm -f /tmp/hdc1.img; touch /tmp/hdc1.img
-               are recommended to specify file "/tmp/hdc1.img" for <dst_dev>
+       <dst_dev> is a file: File must exist and it must be at least the size
+               as <src_dev>. If it is larger, the trailing data will remain
+               unchanged. You can create blank file of size 123456789 by:
+                       dd if=/dev/zero of=/tmp/outimg bs=1 count=1 seek=$[123456789-1]
+               The size of the original <src_dev> can be queried by:
+                       hdparm -g <src_dev>
+               Be aware the size "sectors" is incorrectly the size in bytes,
+               depending on your Linux kernel version. dd(1) command above
+               requires the bytes size (use "bs=512" to use sectors value).
 
 All the numbers are always expressed as sector (that means 512 bytes)
 number/count!