about Software RAID

boot loader

lilo

• ファイルシステムにXFSを使う等で、OSインストール時にliloを選択した場合はデフォルトで全てのミラーdiskのMBRにliloがインストールされる模様
  • attachment:ubuntu-lilo-raid1.png​
  • /etc/lilo.conf (snip)

    # Specifies the boot device.  This is where Lilo installs its boot
    # block.  It can be either a partition, or the raw device, in which
    # case it installs in the MBR, and will overwrite the current MBR.
    #
    boot=/dev/md1
    
    # This option may be needed for some software RAID installs.
    #
    raid-extra-boot=mbr-only
    
    # Specifies the location of the map file
    #
    map=/boot/map
    
    # Specifies the number of deciseconds (0.1 seconds) LILO should
    # wait before booting the first image.
    #
    delay=20
    
    #
    # Boot up Linux by default.
    #
    default=Linux
    
    image=/vmlinuz
            label=Linux
            read-only
    #       restricted
    #       alias=1
            append="root=/dev/md1  "
            initrd=/initrd.img
    
    image=/vmlinuz.old
            label=LinuxOLD
            read-only
            optional
    #       restricted
    #       alias=2
            append="root=/dev/md1  "
            initrd=/initrd.img.old
    

• 少なくともdiskの先頭10MBは同一
  1. sudo dd if=/dev/sda of=sda count=10240 bs=1024
  2. sudo dd if=/dev/sda of=sdb count=10240 bs=1024
  3. sha1sum sd?

     642aace4e9239c85a011c4f6d643786b78e8e454  sda
     642aace4e9239c85a011c4f6d643786b78e8e454  sdb
     

• RAID5でどうなるかは不明

GRUB

• デフォルトでは一つ目のミラーのMBRのみ、GRUBがセットされるため、二つ目のMBRにもGRUBを入れる必要がある
  • ​ミラクル・リナックス：ブートディスクをソフトウェア RAID 1 (ミラーリング) に構成する際の注意
  • ​nDiki: Debian GRUB でソフトウェアRAID1 ブート設定 (2004-01-05)
  • ​ソフトウェアRAID(RAID1)で2台目のHDDでブートする方法 - うまい棒blog
  • ​ソフトウェアRAID1にgrubをインストールする(メモ) - 夙慧.com

• GRUBのコマンドについて
  • ​Introduction to GNU GRUB
  • ​grubを使おう
  • ​CommandList - GRUB Wiki
• この情報によると、RAID時にGRUBコマンドのデファクトとなっている「install」コマンドではなく「setup」コマンドがbetter？
  • ネット上で主に見つかる手順
    1. df /boot

       Filesystem           1K-blocks      Used Available Use% Mounted on
       /dev/md1               1450192    605532    771572  44% /
       

    2. grep md1 /proc/mdstat

       md1 : active raid1 sda2[0] sdb1[2](S) sdc2[1]
       

    3. sudo grub

       grub> device (hd0) /dev/sdc
       grub> root (hd0,1)
       grub> install /boot/grub/stage1 (hd0) /boot/grub/stage2 p /boot/grub/grub.conf
       

    • こちらの方がbetter？ (未検証)

      grub> root (hd2,1)
      grub> setup (hd2)
      

Ubuntu

• liloと同様に、二つ目のMBRにもGRUBが自動でセットされる模様。GRUB installは不要？
  • /boot/grub/menu.lst (snip)

    ## default num
    # Set the default entry to the entry number NUM. Numbering starts from 0, and
    # the entry number 0 is the default if the command is not used.
    #
    # You can specify 'saved' instead of a number. In this case, the default entry
    # is the entry saved with the command 'savedefault'.
    # WARNING: If you are using dmraid do not use 'savedefault' or your
    # array will desync and will not let you boot your system.
    default         0
    
    ## timeout sec
    # Set a timeout, in SEC seconds, before automatically booting the default entry
    # (normally the first entry defined).
    timeout         3
    
    ## hiddenmenu
    # Hides the menu by default (press ESC to see the menu)
    hiddenmenu
    
    title           Ubuntu 8.04.2, kernel 2.6.24-24-server
    root            (hd0,1)
    kernel          /boot/vmlinuz-2.6.24-24-server root=/dev/md1 ro quiet splash
    initrd          /boot/initrd.img-2.6.24-24-server
    

mdadm

Ubuntu

• ​Ubuntu 8.10 技術概要 | Ubuntu Japanese Team #起動時のデグレードRAID設定

• /etc/initramfs-tools/conf.d/mdadm

  # BOOT_DEGRADED:
  # Do you want to boot your system if a RAID providing your root filesystem
  # becomes degraded?
  #
  # Running a system with a degraded RAID could result in permanent data loss
  # if it suffers another hardware fault.
  #
  # However, you might answer "yes" if this system is a server, expected to
  # tolerate hardware faults and boot unattended.
  
  BOOT_DEGRADED=false
  

  • viなどでこのファイルを直接編集しても、反映されない模様。以下のdpkg-reconfigure mdadmから設定する必要がある。
• /etc/mdadm/mdadm.conf

  # instruct the monitoring daemon where to send mail alerts
  MAILADDR root
  

• /etc/default/mdadm

  # AUTOCHECK:
  #   should mdadm run periodic redundancy checks over your arrays? See
  #   /etc/cron.d/mdadm.
  AUTOCHECK=true
  
  # START_DAEMON:
  #   should mdadm start the MD monitoring daemon during boot?
  START_DAEMON=true
  

  • /etc/cron.d/mdadm

    # By default, run at 01:06 on every Sunday, but do nothing unless the day of
    # the month is less than or equal to 7. Thus, only run on the first Sunday of
    # each month. crontab(5) sucks, unfortunately, in this regard; therefore this
    # hack (see #380425).
    6 1 * * 0 root [ -x /usr/share/mdadm/checkarray ] && [ $(date +\%d) -le 7 ] && /usr/share/mdadm/checkarray --cron --all --quiet
    

dpkg-reconfigure mdadm

• [ ... ] がデフォルト値

• sudo dpkg-reconfigure mdadm
  1. /etc/default/mdadm AUTOCHECK

      ┌───────────────────────────┤ Configuring mdadm ├
      │                                                                           │
      │ If your kernel supports it (>> 2.6.14), mdadm can periodically check the  │
      │ redundancy of your MD arrays (RAIDs). This may be a resource-intensive    │
      │ process, depending on your setup, but it could help prevent rare cases    │
      │ of data loss. Note that this is a read-only check unless errors are       │
      │ found; if errors are found, mdadm will try to correct them, which may     │
      │ result in write access to the media.                                      │
      │                                                                           │
      │ The default, if turned on, is to run the checks on the first Sunday of    │
      │ every month at 01:06 o'clock.                                             │
      │                                                                           │
      │ Should mdadm run monthly redundancy checks of the MD arrays?              │
      │                                                                           │
      │                   [<Yes>]                      <No>                       │
      │                                                                           │
      └──────────────────────────────────────
     

  2. /etc/default/mdadm START_DAEMON

       ┌──────────────────────────┤ Configuring mdadm ├
     ─│                                                                         │
       │ The MD (RAID) monitor daemon sends email notifications in response to   │
       │ important MD events (such as a disk failure). You probably want to      │
       │ enable it.                                                              │
       │                                                                         │
       │ Do you want to start the MD monitoring daemon?                          │
       │                                                                         │
       │                   [<Yes>]                      <No>                     │
       │                                                                         │
       └──────────────────────────────────────
     

  3. /etc/mdadm/mdadm.conf MAILADDR

        ┌─────────────────────────┤ Configuring mdadm ├─
     ─ │ Please enter the email address of the user who should get the email   │
        │ notification for important MD events.                                 │
        │                                                                       │
        │ Recipient for email notifications:                                    │
        │                                                                       │
        │ root_________________________________________________________________ │
        │                                                                       │
        │                                <Ok>                                   │
        │                                                                       │
        └─────────────────────────────────────
     

  4. /etc/initramfs-tools/conf.d/mdadm BOOT_DEGRADED

      ┌───────────────────────────┤ Configuring mdadm ├
      │                                                                           │
      │ If your root filesystem is on a RAID, and a disk is missing at boot, it   │
      │ can either boot with the degraded array, or hold the system at a          │
      │ recovery shell.                                                           │
      │                                                                           │
      │ Running a system with a degraded RAID could result in permanent data      │
      │ loss if it suffers another hardware fault.                                │
      │                                                                           │
      │ If you do not have access to the server console to use the recovery       │
      │ shell, you might answer "yes" to enable the system to boot unattended.    │
      │                                                                           │
      │ Do you want to boot your system if your RAID becomes degraded?            │
      │                                                                           │
      │                    <Yes>                      [<No>]                      │
      │                                                                           │
      └──────────────────────────────────────
     

  • apply settings... (liloを使っている場合)

     * Stopping MD monitoring service mdadm --monitor                        [ OK ]
    Generating array device nodes... done.
     Removing any system startup links for /etc/init.d/mdadm-raid ...
    update-initramfs: Generating /boot/initrd.img-2.6.24-24-server
    Warning: LBA32 addressing assumed
    Added Linux *
    Added LinuxOLD
    The Master boot record of  /dev/sda  has been updated.
    Warning: /dev/sdb is not on the first disk
    The Master boot record of  /dev/sdb  has been updated.
    2 warnings were issued.
     * Starting MD monitoring service mdadm --monitor                        [ OK ]