Document usage of version0.91 superblock.

diff --git a/ChangeLog b/ChangeLog
index 4a05767ffef52955ea39ad50239386aef23047ee..8c14d556e5a7469d0f157b86d9fcbca75171aa79 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,6 @@
+Changes Prior to 2.5.3 release
+    -   Document v0.91 superblocks in md.4
+
 Changes Prior to 2.5.2 release
     -   Fix problem with compiling with gcc-2 compilers
     -   Fix compile problem of post-incrmenting a variable in a macro arg.

diff --git a/md.4 b/md.4
index d22ded4231ec017e4d16454b997062dd2e5e8096..cd000651b65f5d95b3c2802ec48419f8bd82bd42 100644 (file)
--- a/md.4
+++ b/md.4
@@ -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