From 224228a2a4db8f433e4ae8fc827e231e095aca45 Mon Sep 17 00:00:00 2001 From: Coly Li 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 Cc: NeilBrown Cc: Jes Sorensen Cc: Paul Menzel Cc: Wols Lists Cc: Nix --- mdadm.8.in | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mdadm.8.in b/mdadm.8.in index 6b63bb4..bba4e25 100644 --- a/mdadm.8.in +++ b/mdadm.8.in @@ -2772,6 +2772,12 @@ option and it is transparent for assembly feature. .IP \(bu 4 Roaming between Windows(R) and Linux systems for IMSM metadata is not supported during grow process. +.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 -- 2.16.4