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[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 <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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5 changed files with 49 additions and 8 deletions
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@ -51,6 +51,30 @@ superblock can be autodetected and run at boot time.
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The kernel parameter "raid=partitionable" (or "raid=part") means
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that all auto-detected arrays are assembled as partitionable.
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Boot time assembly of degraded/dirty arrays
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-------------------------------------------
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If a raid5 or raid6 array is both dirty and degraded, it could have
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undetectable data corruption. This is because the fact that it is
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'dirty' means that the parity cannot be trusted, and the fact that it
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is degraded means that some datablocks are missing and cannot reliably
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be reconstructed (due to no parity).
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For this reason, md will normally refuse to start such an array. This
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requires the sysadmin to take action to explicitly start the array
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desipite possible corruption. This is normally done with
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mdadm --assemble --force ....
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This option is not really available if the array has the root
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filesystem on it. In order to support this booting from such an
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array, md supports a module parameter "start_dirty_degraded" which,
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when set to 1, bypassed the checks and will allows dirty degraded
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arrays to be started.
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So, to boot with a root filesystem of a dirty degraded raid[56], use
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md-mod.start_dirty_degraded=1
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Superblock formats
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------------------
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