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<TITLE>Root RAID HOWTO cookbook: Configuring the Production RAID system.</TITLE>
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<H2><A NAME="s5">5. Configuring the Production RAID system.</A></H2>
<P>
<H2><A NAME="ss5.1">5.1 System specs.</A>
Two systems with identical motherboards were configured.</H2>
<P>
<PRE>
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
</PRE>
The disk drives are designated by linux as 'sda' through 'sdd' on the raid5
system and 'hda' and 'hdc' on the raid1 system.
<P>
<H2><A NAME="ss5.2">5.2 Partitioning the hard drives.</A>
</H2>
<P>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.
<PRE>
<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
</PRE>
The sdx2 and hdx3 partitions were switched to 'swap' after developing
this utility. I could have done it on another machine, however,
the libraries and kernels are all about a year or more out of date
on my other linux boxes and I preferred to build it on the target machine.
<P>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.
<UL>
<LI> If any single hard drive fails, the boot will abort, and
the rescue system will run. Examination of the screen
message or /dos<I>x</I>/raidboot/raidstat.ro will tell the operator
the status of the failed array.</LI>
<LI> 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 <I>x</I>da 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:
<PRE>
"/sbin/mkraid /etc/raid<it/x/.conf -f --only-superblock"
</PRE>
to rebuild the remaining superblock(s).
</LI>
<LI> Once this is done, then
<PRE>
mdadd -ar
</PRE>
</LI>
<LI> 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.
<PRE>
cat /proc/mdstat | grep md0 > /dosx/raidboot/raidgood.ref
shutdown -r now
</PRE>
to do a clean reboot, and the system is up again.</LI>
</UL>
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