Redundant Array of Independent Disks, originally Redundant Array of Inexpensive Disks is a storage technology that combines multiple disk drive components into a logical unit.
Disk arrays stripe data across multiple disks and access them in parallel to achieve:
Higher data transfer rates on large data accesses and
Higher I/O rates on small data accesses.
RAID 0 Block-level striping without parity or mirroring.
RAID 1 Mirroring without parity or striping.
RAID 2 Bit-level striping with dedicated Hamming-code parity.
RAID 3 Byte-level striping with dedicated parity.
RAID 4 Block-level striping with dedicated parity.
RAID 5 Block-level striping with distributed parity.
RAID 6 Block-level striping with double distributed parity.
RAID 10 Nested RAIDs or hybrid RAIDs are constructed by distributing data over mirrored sets of storage devices.
Mirroring plus striping (striped-mirror, RAID-1+0 or RAID-10)
The combination of striping above mirroring is called a striped-mirror layout. Putting mirroring below striping mirrors each column of the stripe. If there are multiple sub disks per column, each subdisk can be mirrored individually instead of each column. A striped-mirror volume is an example of a layered volume.
Level Description Minimum # of disks
RAID 0+1 Top Level RAID 1, Bottom Level RAID 0. 3
RAID 1+0 Top Level RAID 0, Bottom Level RAID 1. 4
RAID 5+0 Top Level RAID 0, Bottom Level RAID 5. 6
RAID 5+1 Top Level RAID 1, Bottom Level RAID 5. 6
RAID 6+0 Top Level RAID 0, Bottom Level RAID 6. 8
RAID 6+1 Top Level RAID 1, Bottom Level RAID 6. 8
RAID 1+0+0 RAID 0 RAID 0 RAID 1 8
Software RAID - the RAID task runs on the CPU of your computer system.
Hardware RAID - solution has its own processor and memory to run the RAID application.
RAID in RHEL 6
The minimum number of software RAID partitions required for each RAID level:
• RAID 0,1,10 – 2 partitions
• RAID 4,5 – 3 partitions
• RAID 6 – 4 partitions
Make 4 partitions of each 1GB
Change System ID as fd to Linux raid autodetect
mdadm -C /dev/md0 -l 5 -n 3 /dev/sdb1 /dev/sdb2 /dev/sdb3
/dev/md0 /raid5 ext4 defaults 0 0
mdadm --detail /dev/md0
#set faulty partition
mdadm -f /dev/md0 /dev/sdb3
mdadm: set /dev/sdb3 faulty in /dev/md0
#add new raid partition
mdadm -a /dev/md0 /dev/sdb4
mdadm: added /dev/sdb4
#remove faulty raid partition
mdadm -r /dev/md0 /dev/sdb3
mdadm: hot removed /dev/sdb3 from /dev/md0