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== RAID 1 and mdadm ==

'''This is a "How to" setup for RAID 1 on Linux.''' It is applied to Debian sarge, however through the use of mdadm (multiple devices admin) it should be able to work on various Linux installs.


=== RAID 1 setup with a NEW install of Debian Sarge ===
Two hard disks of 2gb in total each were setup with RAID. This is done through some careful looking in the Debian Install process.
* Make sure also to Choose - '''linux26''' when booting the Debian Install CD
* Follow the install procedure for Creating Partitions VERY carefully.
* The key point is - when creating a volume, do not choose ext3 -> choose "RAID Volume" for Both hard disks. 
* From the install process it is possible to get the RAID 1 array working perfectly. Note: LVM is NOT used.


=== General Information on Managing RAID ===

mdadm is the tool used to control and manage the RAID array.
 mdadm -D /dev/md0   //Show the details of the md0 array
 mdadm -E /dev/sda1 //Examine the Hard Disk sda1
 cat /proc/mdstat    //Shows the RAID array. [UU]=2 disks are fine. [_U]=1 disk needsss rebuilding
 mdadm --examine --scan //Shows the disks and their array. This information should be in the config file /etc/mdadm/mdadm.conf


=== Monitoring a RAID Array ===
 ps -eaf  //It should show the Monitor already! - /sbin/mdadm -F -i /var/run/mdadm.pid -m root -f -s
 //To monitor manually ->
 mdadm --monitor --mail=root --delay=300 /dev/md0
 nohup mdadm --monitor --mail=sysadmin --delay=300 /dev/md0 &  //The & will background the monitoring


=== Prepare BOTH Hard Disks so EITHER one will boot via Grub ===

This MUST also be DONE after REBUILDING an ARRAY!!! <br>
The MBR has to be reinstalled after having replaced the broken disk: 

 //For Disk 1
 grub 
 device (hd0) /dev/sda 
 root (hd0,0) 
 setup (hd0) 
 
 //For Disk 2
 grub 
 device (hd1) /dev/sdb 
 root (hd1,0) 
 setup (hd1) 

=== How to Rebuild an Array: ===

 mdadm --add /dev/md0 /dev/sda1
 mdadm --add /dev/md0 /dev/sdb1
 //chose which ever one is necessary
 //'''MAKE SURE TO DO THE GRUB BOOT LOADER - OTHERWISE PC WONT BOOT!!!!!!!!!!!'''

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Further Information can be found at: <br>
http://www.networknewz.com/2003/0113.html <br>
http://www.linuxmanpages.com/man8/mdadm.8.php <br>
http://www.planamente.ch/emidio/pages/linux_howto_root_lvm_raid.php#Creating%20RAID%20devices  //Excellent <br>