LFCS objective: Create and manage RAID devices

RAID.md

RAID

Redundant Array of Independent Disks

• A glance at what RAID is. /RAID is not a backup
• Overview of mdadm command
• Creating RAID 0 and RAID 5 Array
• Automounting RAID array at boot

Additional

• We will look at adding and removing disk from array
• Removing RAID Array

LEVEL	0	1	5	6
.	striping	mirroring	parity striping	double parity
Min. disk required	2	2	3	4

• RAID 5 supports a single disk failure.
• RAID 6 supports upto 2 disk failures.

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yum install mdadm

General structure of mdadm command,

mdadm [mode] <raiddevice> [options] <component-devices>

if no mode is specified it will default to --manage. Note that the RAID device comes before component devices.

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(I will be referring to the RAID array as /dev/md0. All commands are run as root user)

• Create level 0 RAID with 2 active devices and 1 spare

mdadm --create /dev/md0 --level=0 --raid-devices=2 \
      /dev/sdb1 /dev/sdb2 --spare=1 /dev/sdb3

Note : we explicitly specify the number of disks that are going to be used in our array

• View information on RAID array

mdadm --detail /dev/md0
cat /proc/mdstat

• Mark a disk faulty

madam /dev/md0 --fail /dev/sdb1

• Remove disk from array ( should not be active)

mdadm /dev/md0 --remove /dev/sdb1

• Add spare to array

mdadm /dev/md0 --add /dev/sdb2

• Save configuration

mdadm --detail --scan >> /etc/mdadm.conf

• Add RAID array from configuration

mdadm --assemble --scan

• Remove a RAID array: make sure the drive is unmounted first.

mdam --stop /dev/md0

Then remove the entry from /etc/mdadm.conf

• Grow RAID ARRAY:

mdadm --add /dev/md0 /dev/sdb2
mdadm --grow /dev/md0 --raid-devices=4  

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Shortcut discussed

Vim shortcut we discussed :

• : set nu or : set number to show line number
• LINE + G or : LINE to jump to LINE
• $ to move to end of line
• gg to move to the end of a file
• G to move to the start of a file