R.A.I.D.What is R.A.I.D.?S.L.E.D.Arrays of Inexpensive DisksRedundant Arrays of Inexpensive DisksRAID 0 – Data StripingRAID 1 - MirroringRAID 2 – Hamming CodeSlide 9RAID 3 – Single Check DiskSlide 11RAID 4 – Independent ReadsRAID 5 – No single check diskConclusionsReferencesR.A.I.D.R.A.I.D.By: Ben SegallBy: Ben SegallWhat is R.A.I.D.?What is R.A.I.D.?In 1987, Patterson, Gibson and Katz In 1987, Patterson, Gibson and Katz at the University of California at the University of California Berkeley, published a paper entitled Berkeley, published a paper entitled "A Case for Redundant Arrays of "A Case for Redundant Arrays of Inexpensive Disks (RAID)“Inexpensive Disks (RAID)“I/O becoming a performance bottleneckI/O becoming a performance bottleneckS.L.E.D.S.L.E.D.S.L.E.D. – Single Large Expensive S.L.E.D. – Single Large Expensive DisksDisksCapacity: goodCapacity: goodPerformance: not-keeping-up with cpuPerformance: not-keeping-up with cpuSolution?Solution?Arrays of Inexpensive DisksArrays of Inexpensive DisksA lot of PC disk developmentA lot of PC disk developmentPatterson, Gibson, and Katz give thumbs Patterson, Gibson, and Katz give thumbs down:down:Used today in what is called RAID level 0 Used today in what is called RAID level 0 (explanation to come)(explanation to come)RedundantRedundant Arrays of Arrays of Inexpensive DisksInexpensive DisksAdding redundancy for error correctionAdding redundancy for error correctionDifferent Levels of R.A.I.D. features vs. Different Levels of R.A.I.D. features vs. performance:performance:(RAID 0) – Data Striping(RAID 0) – Data StripingRAID 1 - MirroringRAID 1 - MirroringRAID 2 – Hamming CodeRAID 2 – Hamming CodeRAID 3 – Single Check Disk per GroupRAID 3 – Single Check Disk per GroupRAID 4 – Independent Reads/WritesRAID 4 – Independent Reads/WritesRAID 5 – No Single Check DiskRAID 5 – No Single Check DiskRAID 0 – Data StripingRAID 0 – Data StripingNot technically a Not technically a RRAID levelAID levelVery good performance, but at a price…Very good performance, but at a price…Recommended ApplicationsRecommended 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 bandwidthRAID 1 - MirroringRAID 1 - MirroringWith greater reliability comes greater With greater reliability comes greater overheadoverheadRecommended ApplicationsRecommended ApplicationsAccounting Accounting Payroll Payroll Financial Financial Any application requiring very high Any application requiring very high availability availabilityRAID 2 – Hamming CodeRAID 2 – Hamming CodeUses bit-level striping and Uses bit-level striping and hamming code ECC in an hamming code ECC in an effort to reduce overheadeffort to reduce overheadExample…Example…Massive disk requirements Massive disk requirements and poor performance on and poor performance on small data kept this RAID small data kept this RAID level more theoretical level more theoretical then practicalthen practicalRAID 2 – Hamming CodeRAID 2 – Hamming CodeRAID 3 – Single Check DiskRAID 3 – Single Check DiskBYTE level striping and XOR ECC allows for BYTE level striping and XOR ECC allows for one check disk: lowest overhead possibleone check disk: lowest overhead possibleExample… Example… A:0101 XOR B:0011 = Check:0110A: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 Parity (Check) drive becomes a bottleneck with heavy I/Owith heavy I/ORAID 3 – Single Check DiskRAID 3 – Single Check DiskXOR ExampleA XOR B Result0 0 01 0 10 1 11 1 0RAID 4 – Independent ReadsRAID 4 – Independent ReadsJust like RAID 3 but stripes on the Just like RAID 3 but stripes on the filefile levellevelFast reads: theoretically 1 per disk Fast reads: theoretically 1 per disk concurrentlyconcurrentlySlow writes: have to read Slow writes: have to read corresponding sectors on each disk corresponding sectors on each disk to calculate new parityto calculate new parityRAID 5 – No single check RAID 5 – No single check diskdiskCheck disk information is distributed across Check disk information is distributed across all data disks – no more check disk all data disks – no more check disk bottleneckbottleneckRecommended ApplicationsRecommended 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 levelConclusionsConclusionsRAID offers a cost effective RAID offers a cost effective alternative to SLED through the use alternative to SLED through the use of data striping, mirroring, and parityof data striping, mirroring, and parityDifferent RAID “levels” can be chosen Different RAID “levels” can be chosen to suit different functions for the to suit different functions for the computer.computer.ReferencesReferencesschool paper: school paper: http://www.cs.ucf.edu/courses/cda5106/summer03/phttp://www.cs.ucf.edu/courses/cda5106/summer03/papers/raid-patterson88.pdfapers/raid-patterson88.pdf flash animations: flash animations: http://www.acnc.com/04_00.htmlhttp://www.acnc.com/04_00.html what is RAID?: http://www.uni-what is RAID?: http://www.uni-mainz.de/~neuffer/scsi/what_is_raid.html mainz.de/~neuffer/scsi/what_is_raid.html RAID info – a different approach: RAID info – a different approach: http://www.arstechnica.com/paedia/r/raid-1.html