From 6ff8d8ec06690f4011a6c3ad9e0759b9094f0601 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Fri, 6 Jan 2006 00:20:15 -0800 Subject: [PATCH] md: allow dirty raid[456] arrays to be started at boot See patch to md.txt for more details Signed-off-by: Neil Brown Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/md.txt | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) (limited to 'Documentation') diff --git a/Documentation/md.txt b/Documentation/md.txt index 23e6cce..1dd0fb6 100644 --- a/Documentation/md.txt +++ b/Documentation/md.txt @@ -51,6 +51,30 @@ superblock can be autodetected and run at boot time. The kernel parameter "raid=partitionable" (or "raid=part") means that all auto-detected arrays are assembled as partitionable. +Boot time assembly of degraded/dirty arrays +------------------------------------------- + +If a raid5 or raid6 array is both dirty and degraded, it could have +undetectable data corruption. This is because the fact that it is +'dirty' means that the parity cannot be trusted, and the fact that it +is degraded means that some datablocks are missing and cannot reliably +be reconstructed (due to no parity). + +For this reason, md will normally refuse to start such an array. This +requires the sysadmin to take action to explicitly start the array +desipite possible corruption. This is normally done with + mdadm --assemble --force .... + +This option is not really available if the array has the root +filesystem on it. In order to support this booting from such an +array, md supports a module parameter "start_dirty_degraded" which, +when set to 1, bypassed the checks and will allows dirty degraded +arrays to be started. + +So, to boot with a root filesystem of a dirty degraded raid[56], use + + md-mod.start_dirty_degraded=1 + Superblock formats ------------------ -- cgit v1.1