File 1002-mdadm.8-add-note-information-for-raid0-growing-opera.patch of Package mdadm.14070

From 224228a2a4db8f433e4ae8fc827e231e095aca45 Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Thu, 19 Dec 2019 18:08:05 +0800
Subject: [PATCH v3] mdadm.8: add note information for raid0 growing operation
Patch-mainline: Not yet, waiting for maintainer to merge
References: bsc#1129900

When growing a raid0 device, if the new component disk size is not
big enough, the grow operation may fail due to lack of backup space.

The minimum backup space should be larger than
        LCM(old, new) * chunk-size * 2
where LCM() is the least common multiple of the old and new count of
component disks, and "* 2" comes from the fact that mdadm refuses to
use more than half of a spare device for backup space.

There are users reporting such failure when they grew a raid0 array
with small component disk. Neil Brown points out this is not a bug
and how the failure comes. This patch adds note information into
mdadm(8) man page in the Notes part of GROW MODE section, to explain
the minimum size requirement of new component disk size or external
backup size.

Signed-off-by: Coly Li <colyli@suse.de>
Cc: NeilBrown <neilb@suse.de>
Cc: Jes Sorensen <jsorensen@fb.com>
Cc: Paul Menzel <pmenzel@molgen.mpg.de>
Cc: Wols Lists <antlists@youngman.org.uk>
Cc: Nix <nix@esperi.org.uk>
---
 mdadm.8.in | 6 ++++++
 1 file changed, 6 insertions(+)

Index: mdadm-4.0/mdadm.8.in
===================================================================
--- mdadm-4.0.orig/mdadm.8.in
+++ mdadm-4.0/mdadm.8.in
@@ -2732,9 +2732,17 @@ Interrupting a grow operation is not rec
 has not been fully tested for Intel's IMSM container format yet.
 
 .PP
-Note: Intel's native checkpointing doesn't use
+Note:
+.IP \(bu 4
+Intel's native checkpointing doesn't use
 .B --backup-file
 option and it is transparent for assembly feature.
+.IP \(bu 4
+When growing a raid0 device, the new component disk size (or external
+backup size) should be larger than LCM(old, new) * chunk-size * 2,
+where LCM() is the least common multiple of the old and new count of
+component disks, and "* 2" comes from the fact that mdadm refuses to
+use more than half of a spare device for backup space.
 
 .SS SIZE CHANGES
 Normally when an array is built the "size" is taken from the smallest