btrfs-progs: docs: Add warning for build RAID btrfs on partions from the same device

Quite a common sense for any RAID-like multi-device setup, just in case.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/Documentation/mkfs.btrfs.asciidoc b/Documentation/mkfs.btrfs.asciidoc
index 7d19a14..6515e14 100644 (file)
--- a/Documentation/mkfs.btrfs.asciidoc
+++ b/Documentation/mkfs.btrfs.asciidoc
@@ -271,6 +271,10 @@ There are the following block group types available:
 | RAID6   | 1            | 2              | 3 to N - 2 | 3/any ^(see note 3)^
 |=============================================================
 
+WARNING: It's not recommended to build btrfs with RAID0/1/10/5/6 prfiles on
+partitions from the same device.  Neither redundancy nor performance will be
+improved.
+
 'Note 1:' DUP may exist on more than 1 device if it starts on a single device and
 another one is added. Since version 4.5.1, *mkfs.btrfs* will let you create DUP
 on multiple devices.