Bug#442874: mdadm: --write-mostly does nothing if device is re-added using --add

[Jens Thiele]

Package: mdadm
Version: 2.6.2-2
Severity: normal


When using: "mdadm --manage /dev/md0 --add --write-mostly somedev"
to re-add a device that previously did not use "write-mostly" to a raid1,
the "--write-mostly" does not have any effect.

Probably this option is stored in the superblock => to make it work
mdadm would have to change the superblock?

Of course it would be nice if mdadm could be fixed. Otherwise it seems
you have to clear the superblock and do a full resync just to change
the "write-mostly" setting (probably one bit in the superblock ;-)
But perhaps it is good enough to mention this in the man page.

Maybe adding something like:
"(note: if --add is used to re-add a device --write-mostly doesn't have any effect)"
to the description of the "--write-mostly" option.

-- Package-specific info:

-- System Information:
Debian Release: lenny/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: i386 (i686)

Kernel: Linux 2.6.21-2-686-imq-raid (SMP w/2 CPU cores)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages mdadm depends on:
ii  debconf [debconf-2.0]         1.5.14     Debian configuration management sy
ii  libc6                         2.6.1-1+b1 GNU C Library: Shared libraries
ii  lsb-base                      3.1-24     Linux Standard Base 3.1 init scrip
ii  makedev                       2.3.1-83   creates device files in /dev

-- debconf information:
  mdadm/autostart: true
* mdadm/initrdstart: all
  mdadm/initrdstart_notinconf: false
  mdadm/initrdstart_msg_errexist:
  mdadm/initrdstart_msg_intro:
  mdadm/initrdstart_msg_errblock:
* mdadm/start_daemon: true
* mdadm/mail_to: root
  mdadm/initrdstart_msg_errmd:
  mdadm/initrdstart_msg_errconf:
* mdadm/autocheck: false