On Tuesday July 11, [email protected] wrote:
> >>> Hm, what's superblock 0.91? It is not mentioned in mdadm.8.
> >>>
> >> Not sure, the block version perhaps?
> >>
> > Well yes of course, but what characteristics? The manual only lists
> > 0, 0.90, default
> > 1, 1.0, 1.1, 1.2
> > No 0.91 :(
>
>
> AFAICR superblock version gets raised by 0.01 for the duration of
> reshape, so that non-reshape aware kernels do not try to assemble it
> (and cause data corruption).
Exactly. The following will be in the next mdadm - unless someone
wants to re-write it for me using shorter sentences :-)
NeilBrown
diff .prev/md.4 ./md.4
--- .prev/md.4 2006-06-20 10:01:17.000000000 +1000
+++ ./md.4 2006-07-18 10:14:47.000000000 +1000
@@ -74,6 +74,14 @@ UUID
a 128 bit Universally Unique Identifier that identifies the array that
this device is part of.
+When a version 0.90 array is being reshaped (e.g. adding extra devices
+to a RAID5), the version number is temporarily set to 0.91. This
+ensures that if the reshape process is stopped in the middle (e.g. by
+a system crash) and the machine boots into an older kernel that does
+not support reshaping, then the array will not be assembled (which
+would cause data corruption) but will be left untouched until a kernel
+that can complete the reshape processes is used.
+
.SS ARRAYS WITHOUT SUPERBLOCKS
While it is usually best to create arrays with superblocks so that
they can be assembled reliably, there are some circumstances where an
-
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