RAID Technology CS350 Computer Organization Section 2 Larkin Young Rob Deaderick Amos Painter Josh Ellis

Overview Background –Term coined by researchers at UC-Berkeley –Redundant Array of Inexpensive Disks Basics of RAID –Disk arrays –Logical/physical –Controller (software/hardware)

Techniques/Methods Mirroring Parity XOR = XOR = XOR =

Techniques/Methods (cont’d) Striping

RAID 0 Uses striping –I/O performance gain –No Data redundancy Not fault tolerant Not considered “true” RAID

RAID 1 Uses mirroring –Also known as duplexing Fault tolerant High Disk overhead –Mirroring typically handled system software Simplest RAID design

RAID 2 Error Detection and Correction Parity and Hamming Code –Used to identify and correct errors Hamming Code –Uses parity bits to verify data integrity Parity bits signify oddness of data bits –ECC (Error Correction Code)

RAID 2 Characterized by: –“On the fly” data correction –High Ratio of Data disks to ECC disks –Not a commercially viable solution –High Costs Involved

RAID 3: XOR Exit Hamming Code, Enter XOR (eXclusive OR) XOR in Action: XOR = If ???? 2 XOR = , Then XOR = ???? 2 = Thus we can use XOR results to recover lost data XOR Logic Table A XOR BR esult

RAID 3: Pros and Cons Advantages: High Read/Write Transfer Rates Disk failures don’t slow the system Low Ratio of Data Disks to Parity Disks Disadvantages: Transaction rate slowed by Parity Disk Complex Controller Design Software Implementation –Resource Intensive

RAID 3: Uses Video Production High-end Video and Image Editing Other uses that require high throughput of data

RAID 4 Offshoot of RAID 3 No Striping, Entire files written to individual disks Parity Data created on a sector-by-sector basis

RAID 4: Pros, Cons, and Uses Advantages: Very high read rates –Multiple files read at once Uses: Web Servers, and other high read, low write situations Disadvantages: Very slow write rates –Even small writes fill up parity write queue Inefficient data recovery Even more Complex Controller Design than RAID 3 *Has most of the other Advantages and Disadvantages of RAID 3

RAID 5 Highest Read data transaction rate Medium Write data transaction rate Most complex controller design Used For Server Applications.

RAID 6 Fault tolerance Very complex controller design Very poor write performance

RAID 7 Extremely high cost per MB Fast access times Improved write performance with increasing number of drives

RAID 10 Uses multiple (mirrored) RAID 1 in a single array Data striped across all mirrored sets Very high fault tolerance High performance rate

RAID 10 Characterized by: - each drive duplicated - high implementation cost

RAID 53 Consists of a striped array made up of RAID 3 segments Very expensive Achieves high rate of I/O

RAID 0+1 Acts as a mirrored array whose parts consist of RAID 0 arrays Very expensive Works well in handling images –very high data transfer rate

RAID Not great reliability - one disk failure leaves you left with only the characteristics of a striped array (no fault tolerance)

Conclusion Grown more complex Large price range Huge step forward for industry Not for the masses yet