Redundant Array Of Inexpensive Disk !!!

RAID, also known as Redundant Array of Inexpensive Drives (or Disks).RAID is an term for data storage schemes that divide and/or replicate data among multiple hard drives. RAID can be designed to provide increased data reliability or increased I/O performance, though one goal may compromise the other.

There are total 10 types of RAID levels:

• RAID level 0
• RAID level RAID level 1
• RAID level 2
• RAID level 3
• RAID level 4
• RAID level 5
• RAID level 6
• RAID level 10
• RAID level 50
• RAID level 0+1

Following are commonly used RAID levels :

RAID level	Minmum Hard disks	Chartcteristics & Advantages	Disadvantages
RAID 0 - Striped Set without parity	2 Hard disks	RAID 0 implements a striped disk array, the data is broken down into blocks and each block is written to a separate disk drive I/O performance is greatly improved by spreading the I/O load across many channels and drives Best performance is achieved when data is striped across multiple controllers with only one drive per controller No parity calculation overhead is involved Very simple design Easy to implement	Not a "True" RAID because it is NOT fault - tolerant The failure of just one drive will result in all data in an array being lost Should never be used in mission critical environments
RAID 1 - Mirrored Set (2 disks minimum) without parity.	2 Hard disks	One Write or two Reads possible per mirrored pair Twice the Read transaction rate of single disks, same Write transaction rate as single disks 100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk Transfer rate per block is equal to that of a single disk Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures Simplest RAID storage subsystem design	Highest disk overhead of all RAID types (100%) - inefficient Typically the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended May not support hot swap of failed disk when implemented in "software"
RAID 5	3 Hard disks	Highest Read data transaction rate Medium Write data transaction rate Low ratio of ECC (Parity) disks to data disks means high efficiency Good aggregate transfer rate	Disk failure has a medium impact on throughput Most complex controller design Difficult to rebuild in the event of a disk failure (as compared to RAID level 1) Individual block data transfer rate same as single disk
RAID 10 (nested RAID 1+0)	4 Hard disks	RAID 10 is implemented as a striped array whose segments are RAID 1 arrays RAID 10 has the same fault tolerance as RAID level 1 RAID 10 has the same overhead for fault-tolerance as mirroring alone High I/O rates are achieved by striping RAID 1 segments Under certain circumstances, RAID 10 array can sustain multiple simultaneous drive failures Excellent solution for sites that would have otherwise gone with RAID 1 but need some additional performance boost	Very expensive / High overhead All drives must move in parallel to proper track lowering sustained performance Very limited scalability at a very high inherent cost

Creation OF Software RAID

> Create 3 partition (5gb each)

> Change the ID of Partition to FD. FD is the ID of RAID

> Configure the Raid device

> I m assuming that i have 3 partitions{sda4,5,6} and i m configuring raid level 5

# mdadm -C /dev/md0 -l 5 -n 3 /dev/sda{4,5,6} <-- mdadm stands for multiple disk administration

> Format the raid device 'md0'

# mke2fs -j /dev/md0

> Create a directory and mount it in fstab

# mkdir raid

# vim /etc/fstab

/dev/md0 raid ext3 defaults 0 0

> save and exit

# mount -a

> Now check the status of raid

# mdadm -D /dev/md0

Remove the RAID

# df - Th

# umount raid

> remove the entry of raid from fstab

# mdadm /dev/md0 -f /dev/sda{4,5,6} <-- For making faulty

# mdadm /dev/md0 -r /dev/sda{4,5,6} <--For removing the raid

# mdadm -r /dev/md0 <-- To remove the raid device name

> Now delete the partition and reboot the system