1. R.A.I.D. By: Ben Segall

2. What is R.A.I.D.? In 1987, Patterson, Gibson and Katz at the University of California Berkeley, published a paper entitled "A Case for Redundant Arrays of Inexpensive Disks (RAID) In 1987, Patterson, Gibson and Katz at the University of California Berkeley, published a paper entitled "A Case for Redundant Arrays of Inexpensive Disks (RAID) I/O becoming a performance bottleneck I/O becoming a performance bottleneck

3. S.L.E.D. S.L.E.D. – Single Large Expensive Disks S.L.E.D. – Single Large Expensive Disks Capacity: good Capacity: good Performance: not-keeping-up with cpu Performance: not-keeping-up with cpuSolution?

4. Arrays of Inexpensive Disks A lot of PC disk development A lot of PC disk development Patterson, Gibson, and Katz give thumbs down: Patterson, Gibson, and Katz give thumbs down: Used today in what is called RAID level 0 (explanation to come) Used today in what is called RAID level 0 (explanation to come)

5. Redundant Arrays of Inexpensive Disks Adding redundancy for error correction Adding redundancy for error correction Different Levels of R.A.I.D. features vs. performance: Different Levels of R.A.I.D. features vs. performance: (RAID 0) – Data Striping (RAID 0) – Data Striping RAID 1 - Mirroring RAID 1 - Mirroring RAID 2 – Hamming Code RAID 2 – Hamming Code RAID 3 – Single Check Disk per Group RAID 3 – Single Check Disk per Group RAID 4 – Independent Reads/Writes RAID 4 – Independent Reads/Writes RAID 5 – No Single Check Disk RAID 5 – No Single Check Disk

6. RAID 0 – Data Striping Not technically a RAID level Not technically a RAID level Very good performance, but at a price… Very good performance, but at a price… Recommended Applications Recommended Applications Video Production and Editing Video Production and Editing Image Editing Image Editing Pre-Press Applications Pre-Press Applications Any application requiring high bandwidth Any application requiring high bandwidth

7. RAID 1 - Mirroring With greater reliability comes greater overhead With greater reliability comes greater overhead Recommended Applications Recommended Applications Accounting Accounting Payroll Payroll Financial Financial Any application requiring very high availability Any application requiring very high availability

8. RAID 2 – Hamming Code Uses bit-level striping and hamming code ECC in an effort to reduce overhead Uses bit-level striping and hamming code ECC in an effort to reduce overhead Example… Example… Massive disk requirements and poor performance on small data kept this RAID level more theoretical then practical Massive disk requirements and poor performance on small data kept this RAID level more theoretical then practical

9. RAID 2 – Hamming Code

10. RAID 3 – Single Check Disk BYTE level striping and XOR ECC allows for one check disk: lowest overhead possible BYTE level striping and XOR ECC allows for one check disk: lowest overhead possible Example… Example… A:0101 XOR B:0011 = Check:0110 A:0101 XOR B:0011 = Check:0110 A is gone? A is gone? B:0011 XOR Check:0110 = 0101 (A) B:0011 XOR Check:0110 = 0101 (A) Parity (Check) drive becomes a bottleneck with heavy I/O Parity (Check) drive becomes a bottleneck with heavy I/O

11. RAID 3 – Single Check Disk XOR Example A XOR BResult 000 101 011 110

12. RAID 4 – Independent Reads Just like RAID 3 but stripes on the file level Just like RAID 3 but stripes on the file level Fast reads: theoretically 1 per disk concurrently Fast reads: theoretically 1 per disk concurrently Slow writes: have to read corresponding sectors on each disk to calculate new parity Slow writes: have to read corresponding sectors on each disk to calculate new parity

13. RAID 5 – No single check disk Check disk information is distributed across all data disks – no more check disk bottleneck Check disk information is distributed across all data disks – no more check disk bottleneck Recommended Applications Recommended Applications File and Application servers File and Application servers Database servers Database servers WWW, E-mail, and News servers WWW, E-mail, and News servers Intranet servers Intranet servers Most versatile RAID level Most versatile RAID level

14. Conclusions RAID offers a cost effective alternative to SLED through the use of data striping, mirroring, and parity RAID offers a cost effective alternative to SLED through the use of data striping, mirroring, and parity Different RAID levels can be chosen to suit different functions for the computer. Different RAID levels can be chosen to suit different functions for the computer.

15. References school paper: http://www.cs.ucf.edu/courses/cda5106/summer03/pap ers/raid-patterson88.pdf school paper: http://www.cs.ucf.edu/courses/cda5106/summer03/pap ers/raid-patterson88.pdf http://www.cs.ucf.edu/courses/cda5106/summer03/pap ers/raid-patterson88.pdf http://www.cs.ucf.edu/courses/cda5106/summer03/pap ers/raid-patterson88.pdf flash animations: http://www.acnc.com/04_00.html flash animations: http://www.acnc.com/04_00.htmlhttp://www.acnc.com/04_00.html what is RAID?: http://www.uni- mainz.de/~neuffer/scsi/what_is_raid.html what is RAID?: http://www.uni- mainz.de/~neuffer/scsi/what_is_raid.htmlhttp://www.uni- mainz.de/~neuffer/scsi/what_is_raid.htmlhttp://www.uni- mainz.de/~neuffer/scsi/what_is_raid.html RAID info – a different approach: http://www.arstechnica.com/paedia/r/raid-1.html RAID info – a different approach: http://www.arstechnica.com/paedia/r/raid-1.html http://www.arstechnica.com/paedia/r/raid-1.html