RAID- Redundant Array of Inexpensive Drives

Purpose Provide faster data access and larger storage Provide data redundancy

RAID control Controller-based (hardware): faster, expensive Host-based (software): flexible for smaller volume

Types of RAID RAID 0: use stripe set RAID 1: use mirror set RAID 2: striping (bit level), has Error Control Bit RAID 3: striping (byte level), has Error Control Bit RAID 4: striping (block level), has Error Control Bit RAID 5: RAID 0 + distributed parity on each disk RAID 6: RAID 5 + redundant parity on each disk RAID 0+1: RAID 0 + RAID 1 RAID 10 (RAID 0+1): RAID 1 + RAID 0 RAID 15: RAID 1 + RAID 5 RAID 50: RAID 5 + RAID 0

RAID 0 Min 2 disks Data stored continuously to next disk as an array of stripe (or block) set Multiple read, single write Fast access and larger storage No fault tolerant Good for high bandwidth applications

RAID 1 Min 2 disks Data mirrored to next disk as an array of mirror (or block) set Multiple read, single write (to both disks) Provide data redundancy fault tolerant (for back up), high overhead Good for high availability applications (e.g. log files)

RAID 5 Combine striping and parity check Parity check across disks Parity stored in each disk Parity provides redundancy (if one disk fail, all data and parity can be recovered from other disks) Highest read applications (e.g. database server, other servers)

RAID 0+1 Combine RAID 0 and RAID 1(fault tolerant) Min 4 drives Expensive, high overhead Has data container and mirror container to store data files and control files in database Good for general fileserver

RAID 1+0 (RAID 10) Combine RAID 1(fault tolerant) and RAID 0 Min 4 drives Very expensive, high overhead Has several stripe sets and 1 mirror set to store data files and control files in database Good for database server with high performance and fault tolerance

RAID 15 Combine RAID 1(fault tolerant) and RAID 5 Most robust and fastest RAIDs

RAID 2 Use RAID 0 in bit level Has error correction code (ECC, e.g. Hamming code) for each stripe set to check read/write ECC stored in a separate disk ECC disk is inefficient No commercial applications

RAID 3 Use RAID 0 in byte level Block distributed on several disks Has parity for each block to check read/write parity stored in a separate disk Min 3 disks Good for high throughput applications (e.g. streaming vedio)

RAID 4 Use RAID 0 in block level One block is on one disk Has parity across disks to check read/write parity stored in a separate disk Good for high read applications

RAID 6 Combine striping and parity check Double parity check across disks and within the disk Parity stored in each disk Parity provides redundancy (if 2 disks fail, all data and parity can be recovered from other disks) Highest read applications (e.g. database server, other servers)

RAID 50 Combine RAID 0 and RAID 3 Min 5 disks Same fault tolerance as RAID 3 Boost performance for existing RAID 3