Root RAID HOWTO cookbook

5. Configuring the Production RAID system.

5.1 System specs. Two systems with identical motherboards were configured.

                                  Raid-1          Raid-5
Motherboard:    Iwill P55TU     dual ide        adaptec scsi
Processor:      Intel P200
Disks:                          2ea  7 gig      4 ea Segate 4.2 gig
                                Maxtors         wide scsii

5.2 Partitioning the hard drives.

Since testing a large root mountable RAID array is difficult because of the ckraid re-boot problem, I re-partitioned my swap space to include a smaller RAID partition for testing purposes, sda6,sdb6,sdc6,sdd6, and a small root and /usr/src partition pair for developing and testing the raid kernel and tools. You may find this helpful.

        <bf/DEVELOPMENT SYSTEM - RAID5/
   Device       System          Size    Purpose

  /dev/sda1     dos boot        16 meg  boot partition
* /dev/sda2     extended        130 meg (see below)
  /dev/sda3     linux native    4 gig   primary raid5-1
----------------------sda2------------------------------
* /dev/sda5     linux swap      113 meg SWAP space
* /dev/sda6     linux native    16 meg  test raid5-1
========================================================
  /dev/sdb1     dos boot        16 meg  boot partition duplicate
* /dev/sdb2     extended        130 meg (see below)
  /dev/sdb3     linux native    4 gig   primary raid5-2
----------------------sdb2------------------------------
* /dev/sdb5     linux swap      113 meg SWAP space
* /dev/sdb6     linux native    16 meg  test raid5-2
========================================================
* /dev/sdc2     extended        146 meg (see below)
  /dev/sdc3     linux native    4 gig   primary raid5-3
----------------------sdc2------------------------------
* /dev/sdc5     linux swap      130 meg development root partition
* /dev/sdc6     linux native    16 meg  test raid5-3
========================================================
* /dev/sdd2     extended        146 meg (see below)
  /dev/sdd3     linux native    4 gig   primary raid5-4
----------------------sdd2------------------------------
* /dev/sdd5     linux swap      130 meg development /usr/src
* /dev/sdd6     linux native    16 meg  test raid5-4


        <bf/DEVELOPMENT SYSTEM - RAID1/
   Device       System          Size    Purpose

  /dev/hda1     dos             16meg   boot partition
* /dev/hda2     extended        126m    (see below)
  /dev/hda3     linux           126m    development root partition
  /dev/hda4     linux           6+gig   raid1-1
----------------------hda2------------------------------
* /dev/hda5     linux            26m    test raid1-1
* /dev/hda6     linux swap      100m
========================================================

  /dev/hdc1     is simply an exact copy of hda1 so the
                partion can be made active if hda fails
* /dev/hdc2     extended        126m    (see below)
  /dev/hdc3     linux           126m    development /usr/src
  /dev/hdc4     linux           6+gig   raid1-2
----------------------hdc2------------------------------
* /dev/hdc5     linux            26m    test raid1-2
* /dev/hdc6     linux swap      100m

The partitioning scheme was chosen so that in the event that any one of the drives fails catastrophically, the system will continue to run and be bootable with minimum effort and NO data loss.

• If any single hard drive fails, the boot will abort, and the rescue system will run. Examination of the screen message or /dosx/raidboot/raidstat.ro will tell the operator the status of the failed array.
• If sda1 (raid5) or hda1 (raid1) fails, the dos backup boot partition must be made 'active' and the bios must recognize the new partition as the boot device or it must be physically be moved to the xda position. Alternatively, the system could be booted from a floppy disk using the initrd image on the remaining backup boot drive. The raid system can then be made active again by issuing:

           "/sbin/mkraid /etc/raid<it/x/.conf -f --only-superblock"
  

  to rebuild the remaining superblock(s).
• Once this is done, then

          mdadd -ar
  

• Examine the status of the array to verify that everything is OK then replace the good array reference with the current status until the failed disk can be repaired or replaced.

          cat /proc/mdstat | grep md0 > /dosx/raidboot/raidgood.ref
  
          shutdown -r now
  

  to do a clean reboot, and the system is up again.