MODULE 3 DATA PROTECTION RAID EMC Proven Professional

MODULE – 3 DATA PROTECTION – RAID EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. Module 3: Data Protection - RAID 1

Module 3: Data Protection – RAID Upon completion of this module, you should be able to: • Describe RAID implementation methods • Describe three RAID techniques • Describe commonly used RAID levels • Describe the impact of RAID on performance • Compare RAID levels based on their cost, performance, and protection EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 2

RAID EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 3

Why RAID? RAID It is a technique that combines multiple disk drives into a logical unit (RAID set) and provides protection, performance, or both. • Due to mechanical components in a disk drive it offers limited • performance An individual drive has a certain life expectancy and is measured in MTBF: 4 For example: If the MTBF of a drive is 750, 000 hours, and there are 1000 drives in the array, then the MTBF of the array is 750 hours (750, 000/1000) • RAID was introduced to mitigate these problems EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 4

RAID Implementation Methods • Software RAID implementation 4 Uses host-based software to provide RAID functionality 4 Limitations 8 Use host CPU cycles to perform RAID calculations, hence impact overall system performance 8 Support limited RAID levels 8 RAID software and OS can be upgraded only if they are compatible • Hardware RAID Implementation 4 Uses a specialized hardware controller installed either on a host or on an array EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 5

RAID Array Components Logical Array (RAID Sets) RAID Controller Hard Disks Host RAID Array EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 6

RAID Techniques • Three key techniques used for RAID are: 4 Striping 4 Mirroring 4 Parity EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 7

RAID Technique – Striping Strip RAID Controller Stripe Host EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 8

RAID Technique – Mirroring Block 0 RAID Controller Block 0 Host EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 9

RAID Technique – Parity 4 D 1 6 D 2 RAID Controller 1 D 3 7 Host D 4 18 P Actual parity calculation is a bitwise XOR operation EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 10

Data Recovery in Parity Technique 4 D 1 6 D 2 RAID Controller ? D 3 7 Host D 4 Regeneration of data when Drive D 3 fails: 4 + 6 + ? + 7 = 18 ? = 18 – 4 – 6 – 7 ? =1 EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 18 P 11

Module 3: Data Protection – RAID Lesson 2: RAID Levels During this lesson the following topics are covered: • Commonly used RAID levels • RAID impacts on performance • RAID comparison • Hot spare EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 12

RAID Levels • Commonly used RAID levels are: 4 RAID 0 – Striped set with no fault tolerance 4 RAID 1 – Disk mirroring 4 RAID 1 + 0 – Nested RAID 4 RAID 3 – Striped set with parallel access and dedicated parity disk 4 RAID 5 – Striped set with independent disk access and a distributed parity 4 RAID 6 – Striped set with independent disk access and dual distributed parity EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 13

RAID 0 C B A Data from host RAID Controller A 1 B 1 C 1 A 2 B 2 C 2 A 3 B 3 C 3 A 4 B 4 C 4 A 5 B 5 C 5 Data Disks EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 14

RAID 1 F E D C B A Data from host RAID Controller A B C Mirror Set EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. D E F Mirror Set 15

Nested RAID – 1+0 C B A Data from host Striping Mirroring A 1 B 1 C 1 Mirror Set A A 1 B 1 C 1 Mirroring A 2 B 2 C 2 Mirror Set B EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. RAID Controller Mirroring A 2 B 2 C 2 A 3 B 3 C 3 Mirror Set C 16

RAID 3 C B A Data from host RAID Controller A 1 B 1 C 1 A 2 B 2 C 2 Data Disks EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. A 3 B 3 C 3 A 4 B 4 C 4 AP BP CP Dedicated Parity Disk 17

RAID 5 C B A Data from host RAID Controller A 1 B 1 C 1 A 2 B 2 C 2 A 3 B 3 CP A 4 BP C 3 AP B 4 C 4 Distributed Parity EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 18

RAID 6 C B A Data from host RAID Controller A 1 B 1 C 1 A 2 B 2 CP A 3 BP CQ AP BQ C 2 AQ B 3 C 3 Dual Distributed Parity EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 19

RAID Impacts on Performance RAID Controller Cp new Cp old = C 4 old - C 4 new + 2 4 A 1 B 1 C 1 1 A 2 B 2 C 2 A 3 B 3 CP 3 A 4 BP C 3 AP B 4 C 4 • In RAID 5, every write (update) to a disk manifests as four I/O • • operations (2 disk reads and 2 disk writes) In RAID 6, every write (update) to a disk manifests as six I/O operations (3 disk reads and 3 disk writes) In RAID 1, every write manifests as two I/O operations (2 disk writes) EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 20

RAID Penalty Calculation Example • Total IOPS at peak workload is 1200 • Read/Write ratio 2: 1 • Calculate disk load at peak activity for: 4 RAID 1/0 4 RAID 5 EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 21

Solution: RAID Penalty • For RAID 1/0, the disk load (read + write) = (1200 x 2/3) + (1200 x (1/3) x 2) = 800 + 800 = 1600 IOPS • For RAID 5, the disk load (read + write) = (1200 x 2/3) + (1200 x (1/3) x 4) = 800 + 1600 = 2400 IOPS EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 22

RAID Comparison RAI Min D disk level s Available storage capacity (%) Read performance Write penalty Mirror Protection 1 2 50 Better than single disk Slower than single disk, because every Moderate write must be committed to all disks 1+0 4 50 Good [(n-1)/n]*100 Fair for random reads and good for sequential reads Poor to fair for small random writes High fair for large, sequential writes Parity (Supports single disk failure) [(n-1)/n]*100 Good for random Fair for random and sequential High sequential writes reads Parity (Supports single disk failure) [(n-2)/n]*100 Good for random Poor to fair for and sequential random and reads sequential writes Parity (Supports two disk failures) 3 5 6 3 3 4 Moderate Very High where n = number of disks EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 23

Suitable RAID Levels for Different Applications • RAID 1+0 4 Suitable for applications with small, random, and write intensive (writes typically greater than 30%) I/O profile 4 Example: OLTP, RDBMS – Temp space • RAID 3 4 Large, sequential read and write 4 Example: data backup and multimedia streaming • RAID 5 and 6 4 Small, random workload (writes typically less than 30%) 4 Example: email, RDBMS – Data entry EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 24

Hot Spare Failed disk RAID Controller Replace failed disk Hot spare EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 25

Module 3: Summary Key points covered in this module: • RAID implementation methods and techniques • Common RAID levels • RAID write penalty • Compare RAID levels based on their cost and performance EMC Proven Professional. Copyright © 2012 EMC Corporation. All Rights Reserved. 26