Raid: Data Striping, Mirroring, Parity; New, used and refurbished

Celerity FC Storage | Host Adapters | Bridges | FC Hubs | FC Rack Systems | Storage Array | Workgroup Solutions | Enterprise Solution |  Raid Overview |  What is Diamond Array Storage
What is ADXT Technology | ATTO iPBridge and Microsoft Windows | ATTO and Apple-Mac Xserve Raid | Fibre Channel Storage Connectivity

ATTO Diamond Array Out performs Nexsan ATAboy2 Array

Introduction | Origins of Raid | Original Raid Levels | Raid Today

Raid Summary:

Raid 0: Striped Disk Array | Raid 1: Mirrored Disk Array | Raid 10: Mirroring and Striping | Raid 0,1: Striping and Mirroring | Raid 3: Striping with dedicated parity disk | Raid 5: Striping and Parity

Comparing Raid Configurations | Raid Set-up Considerations

III. Original RAID Levels
The group outlined six RAID architectures (levels) ranging from “Level 0 RAID” to “Level 5 RAID”. These levels provided alternative ways of achieving storage fault tolerance, increased I/O performance and true scalability.
They used three main building blocks in their architectures:
 

1. Data Striping - Data from the host computer is broken up into smaller chunks and distributed to multiple drives within a RAID array. Each drives storage space is partitioned into stripes. The stripes are interleaved such that the logical storage unit is made up of alternating stripes from each drive. Major benefits are I/O performance and the ability to create large logical volumes. Used in RAID 0.
2. Mirroring. Data from the host computer is duplicated on a block-to-block basis across two disks. If one disk drive fails, the data remains available on the other disk. Used in RAID levels 1 and 1+ 0.
3. Parity. Parity. Data from the host computer is written to multiple drives. One or more drives are assigned to store parity information. In the event of a disk failure, parity information is combined with the remaining data to regenerate the missing information. Used in RAID levels 3, 4 and 5.
RAID 0 plus the five original RAID levels developed by the Berkley scientists (along with the RAID group’s performance, reliability and cost assumptions) are listed as follows:
RAID Level 0
• Striped Disks.
o Performance: Very Good
o Reliability: Poor— Less than a single disk drive (Non-Redundant)
o Cost:: Low
RAID Level 1
• Mirrored Disks.
o Performance: Slightly better than a single drive
o Reliability: Excellent.
o Cost:: High (must purchase 2X disks).
RAID Level 2
• Uses bit interleaving and ECC. (This feature is built in to most modern Disk drives now)
o Performance: Same as RAID level 1 for large I/Os.
On small I/Os it is very bad; have to read all disks; no parallelism.
o Reliability: Good
o Cost:: Cost is better than mirroring with 20% to 40% cost overhead
RAID Level 3
• Uses byte interleaving with parity instead of ECC. Parity data is stored on a dedicated drive.
o Performance: Same as RAID level 0 for reads, Writes are slightly slower.
o Reliability: Good
o Cost:: Cost is 1 additional disk per RAID group
RAID Level 4
• Same as RAID Level 3, but use sector interleaving instead of bit interleaving.
o Performance: Same as RAID level 0 for reads, Writes are slightly slower.
o Reliability: Good
o Cost:: Cost is 1 additional disk per RAID group
RAID: Level 5
• Same as RAID Level 4, but distributes stripe parity across all disks.
o Performance: Writes are slightly faster than RAID 3 and 4, but reads tend to be
considerably slower.
o Reliability: Good
o Cost:: Cost is 1 additional disk per RAID group