CS 61C Great Ideas in Computer Architecture Machine Structures Redundant Arrays of Inexpensive Disks Instructors Randy H Katz David A Patterson http inst eecs Berkeley edu cs61c fa10 01 14 2019 Spring 2011 Lecture 27 1 01 14 2019 Spring 2011 Lecture 27 2 Agenda RAID Administrivia Course Summary Randy Cal Culture Dave Course Evaluation 01 14 2019 Spring 2011 Lecture 27 3 Agenda RAID Administrivia Course Summary Randy Cal Culture Dave Course Evaluation 01 14 2019 Spring 2011 Lecture 27 4 Evolution of the Disk Drive IBM 3390K 1986 01 14 2019 IBM RAMAC 305 1956 Spring 2011 Lecture 27 Apple SCSI 1986 5 Arrays of Small Disks Can smaller disks be used to close gap in performance between disks and CPUs Conventional 4 disk 3 5 designs 5 25 10 Low End 14 High End Disk Array 1 disk design 3 5 01 14 2019 Spring 2011 Lecture 27 6 Replace Small Number of Large Disks with Large Number of Small Disks 1988 Disks Capacity Volume Power Data Rate I O Rate MTTF Cost IBM 3390K 20 GBytes 97 cu ft 3 KW 15 MB s 600 I Os s 250 KHrs 250K IBM 3 5 0061 320 MBytes 0 1 cu ft 11 W 1 5 MB s 55 I Os s 50 KHrs 2K x70 23 GBytes 11 cu ft 1 KW 120 MB s 3900 IOs s Hrs 150K 9X 3X 8X 6X Disk Arrays have potential for large data and I O rates high MB per cu ft high MB per KW but what about reliability 01 14 2019 Spring 2011 Lecture 27 7 RAID Redundant Arrays of Inexpensive Disks Files are striped across multiple disks Redundancy yields high data availability Availability service still provided to user even if some components failed Disks will still fail Contents reconstructed from data redundantly stored in the array Capacity penalty to store redundant info Bandwidth penalty to update redundant info 01 14 2019 Spring 2011 Lecture 27 8 Redundant Arrays of Inexpensive Disks RAID 1 Disk Mirroring Shadowing recovery group Each disk is fully duplicated onto its mirror Very high availability can be achieved Bandwidth sacrifice on write Logical write two physical writes Reads may be optimized Most expensive solution 100 capacity overhead 01 14 2019 Spring 2011 Lecture 27 9 Redundant Array of Inexpensive Disks RAID 3 Parity Disk 10010011 11001101 10010011 logical record Striped physical records P 1 0 1 0 0 0 1 1 P contains sum of other disks per stripe mod 2 parity If disk fails subtract P from sum of other disks to find missing information 01 14 2019 Spring 2011 Lecture 27 1 1 0 0 1 1 0 1 1 0 1 0 0 0 1 1 1 1 0 0 1 1 0 1 10 Redundant Arrays of Inexpensive Disks RAID 4 High I O Rate Parity Insides Insidesof of55 disks disks Example Example small smallread readD0 D0 D5 D5 large large write writeD12D12D15 D15 01 14 2019 D0 D1 D2 D3 P D4 D5 D6 D7 P D8 D9 D10 D11 P D12 D13 D14 D15 P Stripe D16 D17 D18 D19 P D20 D21 D22 D23 P Disk Columns 2011 Lecture 27 Spring Increasing Logical Disk Address 11 Inspiration for RAID 5 RAID 4 works well for small reads Small writes write to one disk Option 1 read other data disks create new sum and write to Parity Disk Option 2 since P has old sum compare old data to new data add the difference to P Small writes are limited by Parity Disk Write to D0 D5 both also write to P disk 01 14 2019 D0 D1 D2 D3 P D4 D5 D6 D7 P Spring 2011 Lecture 27 12 RAID 5 High I O Rate Interleaved Parity Independent Independent writes writes possible possible because becauseof of interleaved interleaved parity parity Example write to D0 D5 uses disks 0 1 3 4 01 14 2019 D0 D1 D2 D3 P D4 D5 D6 P D7 D8 D9 P D10 D11 D12 P D13 D14 D15 P D16 D17 D18 D19 D20 D21 D22 D23 P Disk Columns Lecture 27 Spring 2011 Increasing Logical Disk Addresses 13 Problems of Disk Arrays Small Writes RAID 5 Small Write Algorithm 1 Logical Write 2 Physical Reads 2 Physical Writes D0 D0 D1 D2 D3 old data 1 Read new data P old 2 Read parity XOR XOR 3 Write D0 01 14 2019 D1 4 Write D2 Spring 2011 Lecture 27 D3 P 14 Tech Report Read Round the World December 1987 01 14 2019 Spring 2011 Lecture 27 15 RAID I RAID I 1989 Consisted of a Sun 4 280 workstation with 128 MB of DRAM four dual string SCSI controllers 28 5 25inch SCSI disks and specialized disk striping software 01 14 2019 Spring 2011 Lecture 27 16 RAID II 1990 1993 Early Network Attached Storage NAS System running a Log Structured File System LFS Impact 25 Billion year in 2002 Over 150 Billion in RAID device sold since 1990 2002 200 RAID companies at the peak Software RAID a standard component of modern OSs 01 14 2019 Spring 2011 Lecture 27 17 RAID II 01 14 2019 Spring 2011 Lecture 27 18 RAID Summary Logical to physical block mapping parity striping readmodify write processing Embedded caches and orchestrating data staging between network interfaces parity hardware and file server interfaces Failed disk replacement hot spares background copies and backup Embedded log structured file systems compression on the fly Software complexity dominates hardware 01 14 2019 Spring 2011 Lecture 27 19 Agenda RAID Administrivia Course Summary Randy Cal Culture Dave Course Evaluation 01 14 2019 Spring 2011 Lecture 27 20 Administrivia Final Review Mon 5 2 5 8PM 2050 VLSB Final Exam Mon 5 9 11 30 2 30PM 100 Haas Pavilion Designed for 90 minutes you will have 3 hours Comprehensive particularly problem areas on midterm but focused on course since midterm lecture lab hws and projects are fair game 8 inch x 11 inch crib sheet like midterm 01 14 2019 Spring 2011 Lecture 27 21 Some Survey Results I felt the midterm was 9 Far too difficult 43 Somewhat harder than it should have been 46 Fair 1 A little too easy 1 Far too easy 01 14 2019 Spring 2011 Lecture 27 22 Some Survey Results How much time per week to you spend on average in 61C including lecture discussion and labs 18 10 hours per week 26 11 12 hours per week Berkeley guidelines 3 hours unit 13 13 14 hours per week 24 15 16 hours per week EECS classes often guidelines 10 17 20 hours per week 10 21 hours per week 01 14 2019 Spring 2011 Lecture 27 23 Some Survey Results Rated as Enjoyed and learned a lot Project 4 Processor Design in Logisim Part 2 73 Part 1 60 Logisim Labs 58 C memory management lab 55 TLP and DLP Labs 52 Project 3 Matrix Multiply Performance Improvement Part 2 36 Part 1 35 01 14 2019 Spring 2011 Lecture 27 24 Some Survey Results Did 61C material come up in interviews for internships or …
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