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From 2551061c253b8fd45ee93d1aab3e91d2c7ac9c20 Mon Sep 17 00:00:00 2001
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From: Coly Li <colyli@suse.de>
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Date: Mon, 24 Feb 2020 12:34:09 +0100
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Subject: [RHEL7.9 PATCH 62/77] mdadm.8: add note information for raid0 growing
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operation
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When growing a raid0 device, if the new component disk size is not
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big enough, the grow operation may fail due to lack of backup space.
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The minimum backup space should be larger than:
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LCM(old, new) * chunk-size * 2
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where LCM() is the least common multiple of the old and new count of
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component disks, and "* 2" comes from the fact that mdadm refuses to
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use more than half of a spare device for backup space.
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There are users reporting such failure when they grew a raid0 array
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with small component disk. Neil Brown points out this is not a bug
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and how the failure comes. This patch adds note information into
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mdadm(8) man page in the Notes part of GROW MODE section to explain
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the minimum size requirement of new component disk size or external
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backup size.
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Reviewed-by: Petr Vorel <pvorel@suse.cz>
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Cc: NeilBrown <neilb@suse.de>
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Cc: Jes Sorensen <jsorensen@fb.com>
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Cc: Paul Menzel <pmenzel@molgen.mpg.de>
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Cc: Wols Lists <antlists@youngman.org.uk>
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Cc: Nix <nix@esperi.org.uk>
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Signed-off-by: Coly Li <colyli@suse.de>
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Signed-off-by: Jes Sorensen <jsorensen@fb.com>
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---
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mdadm.8.in | 6 ++++++
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1 file changed, 6 insertions(+)
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diff --git a/mdadm.8.in b/mdadm.8.in
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index 5d00faf..a3494a1 100644
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--- a/mdadm.8.in
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+++ b/mdadm.8.in
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@@ -2768,6 +2768,12 @@ option and it is transparent for assembly feature.
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.IP \(bu 4
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Roaming between Windows(R) and Linux systems for IMSM metadata is not
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supported during grow process.
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+.IP \(bu 4
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+When growing a raid0 device, the new component disk size (or external
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+backup size) should be larger than LCM(old, new) * chunk-size * 2,
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+where LCM() is the least common multiple of the old and new count of
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+component disks, and "* 2" comes from the fact that mdadm refuses to
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+use more than half of a spare device for backup space.
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.SS SIZE CHANGES
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Normally when an array is built the "size" is taken from the smallest
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--
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2.7.5
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