1. © 2009 EMC Corporation. All rights reserved. Intelligent Storage Systems Module 1.4

2. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 2 Module Objectives After completing this module, you will be able to:  Describe components of intelligent storage system  List benefits of intelligent storage system  Explain intelligent cache algorithms and protection  Describe intelligent storage array implementation – High-end storage array – Mid-range storage array

3. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 3 What is an Intelligent Storage System Intelligent Storage Systems are RAID arrays that are:  Highly optimized for I/O processing  Have large amounts of cache for improving I/O performance  Have operating environments that provide: – Intelligence for managing cache – Array resource allocation – Connectivity for heterogeneous hosts – Advanced array based local and remote replication options

4. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 4 Benefits of an Intelligent Storage System Intelligent storage system provides several benefits over a collection of disks in an array (JBOD) or even a RAID arrays: – Increased capacity – Improved performance – Easier data management – Improved data availability and protection – Enhanced Business Continuity support – Improved security and access control

5. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 5 Components of an Intelligent Storage System Host Connectivity FC SAN Front EndBack End Cache Physical Disks Intelligent Storage System

6. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 6 Intelligent Storage System: Front End Host Connectivity Front EndBack End Cache Physical Disks Intelligent Storage System FC SAN Ports Controllers

7. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 7 Front End Command Queuing DCBA DCBA A B C D I/O RequestsI/O Processing Order Front-End Controller Cylinders Without Optimization (FIFO) DBCADCBA A B C D I/O RequestsI/O Processing Order Front-End Controller Cylinders With command queuing

8. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 8 Disk Scheduling  The operating system is responsible for using hardware efficiently — for the disk drives, this means having a fast access time and disk bandwidth.  Access time has two major components – Seek time is the time for the disk are to move the heads to the cylinder containing the desired sector. – Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head.  Minimize seek time  Seek time  seek distance  Disk bandwidth is the total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer.

9. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 9 Disk Scheduling (Cont.)  Several algorithms exist to schedule the servicing of disk I/O requests.  We illustrate them with a request queue (0-199). 98, 183, 37, 122, 14, 124, 65, 67 Head pointer 53

10. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 10 FCFS (First Come, First Served) Illustration shows total head movement of 640 cylinders.

11. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 11 SSTF (Shortest Seek Time First)  Selects the request with the minimum seek time from the current head position.  SSTF scheduling is a form of SJF (Shortest Job First) scheduling; may cause starvation of some requests.  Illustration shows total head movement of 236 cylinders.

12. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 12 SSTF (Cont.) 65, 67, 37, 14, 98, 122, 124, 183

13. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 13 SCAN  The disk arm starts at one end of the disk, and moves toward the other end, servicing requests until it gets to the other end of the disk, where the head movement is reversed and servicing continues.  Sometimes called the elevator algorithm.  Illustration shows total head movement of 208 cylinders.

14. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 14 SCAN (Cont.) 37, 14, 65, 67, 98, 122, 124, 183

15. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 15 C-SCAN (Circular-SCAN)  Provides a more uniform wait time than SCAN.  The head moves from one end of the disk to the other. servicing requests as it goes. When it reaches the other end, however, it immediately returns to the beginning of the disk, without servicing any requests on the return trip.  Treats the cylinders as a circular list that wraps around from the last cylinder to the first one.

16. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 16 C-SCAN (Cont.) 65, 67, 98, 122, 124, 183, 14,37

17. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 17 C-LOOK  Version of C-SCAN  Arm only goes as far as the last request in each direction, then reverses direction immediately, without first going all the way to the end of the disk.

18. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 18 C-LOOK (Cont.) 65, 67, 98, 122, 124, 183, 14,37

19. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 19 Selecting a Disk-Scheduling Algorithm  SSTF is common and has a natural appeal.  SCAN and C-SCAN perform better for systems that place a heavy load on the disk.  Performance depends on the number and types of requests.  Requests for disk service can be influenced by the file-allocation method.  The disk-scheduling algorithm should be written as a separate module of the operating system, allowing it to be replaced with a different algorithm if necessary.  Either SSTF or LOOK is a reasonable choice for the default algorithm.

20. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 20 Intelligent Storage System: Cache Host Connectivity Front EndBack End Cache Physical Disks Intelligent Storage System FC SAN

21. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 21 Write Request Write Operation with Cache Write Request Write-through Cache Write-back Acknowledgement Cache Acknowledgement

22. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 22 Read Request Cache Read Request Cache Data found in cache = ‘Hit’ No data found = ‘Miss’ Read Operation with Cache: ‘Hits’ and ‘Misses’

23. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 23 Cache Management: Algorithms  Least Recently Used (LRU) – Discards least recently used data  Most Recently Used (MRU) – Discards most recently used data New Data Oldest Data

24. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 24 Cache Management: Watermarking LWM HWM 100 % Idle flushing High watermark flushingForced flushing  Manage peak I/O requests “bursts” through flushing/de- staging – Idle flushing, High Watermark flushing and Forced flushing  For maximum performance: – Provide headroom in write cache for I/O bursts

25. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 25 Cache Data Protection  Protecting cache data against failure: – Cache mirroring  Each write to the cache is held in two different memory locations on two independent memory cards – Cache vaulting  Cache is exposed to the risk of uncommitted data loss due to power failure

26. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 26 Intelligent Storage System: Back End Host Connectivity PortsControllers Front EndBack End Cache Physical Disks Intelligent Storage System FC SAN

27. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 27 Intelligent Storage System: Physical Disks Host Connectivity Front EndBack End Cache Physical Disks Intelligent Storage System FC SAN

28. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 28 What the Host Sees – RAID Sets and LUNs Host 1 Host 2 LUN 0 LUN 1 Front EndBack End Cache Physical Disks Intelligent Storage System LUN 0 LUN 1 Connectivity FC SAN

29. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 29 LUN Masking  LUN masking is access control mechanism  Process of masking LUNs from unauthorized access  Implemented on storage arrays  Storage group logical entity that contains one or more LUNs and one host

30. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 30 ISS Implementation: High-end Storage Systems  Also referred as Active-active arrays – I/O’s are serviced through all the available paths  Following are high-end array capabilities: – Large storage capacity – Huge cache to service host I/Os – Fault tolerance architecture – Multiple front-end ports and support to interface protocols – High scalability – Ability to handle large amounts of concurrent I/Os  Designed for large enterprises Host Storage Array Active-Active Configuration Active LUN Controller A Controller B Port

31. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 31 Midrange Storage Systems  Also referred as Active-passive arrays – Host can perform I/Os to LUNs only through active paths – Other paths remain passive till active path fails  Midrange array have two controllers, each with cache, RAID controllers and disks drive interfaces  Designed for small and medium enterprises  Less scalable as compared to high-end array Host Storage Array Active-Passive Configuration Active Passive LUN Controller A Controller B Port

32. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 32 Module Summary Key points covered in this module:  Intelligent Storage Systems features  Components of Intelligent Storage Systems  Cache management algorithms  Intelligent Storage System implementation – High-end storage array – Mid range storage array

33. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 33 Concept in Practice: EMC CLARiiON  Support for UltraFlex technology  Scalable from up to 960 disks  Supports flash drives  Supports different types and sizes of drives, and RAID types (0, 1, 1+0, 3, 5, 6)  Supports up to 16 GB of available cache memory per controller (Storage Processor)  Enhances availability with non disruptive upgrade and failover  Ensures data protection through mirrored write cache and cache vaulting  Supports storage-based local and remote data replication – Through SnapView and MirrorView software

34. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 34 CLARiiON CX-4 Architecture

35. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 35 EMC Symmetrix  Incrementally scalable to 2,400 disks  Supports Flash-based solid-state drives  Dynamic global cache memory (16 GB– 512 GB)  Advanced processing power (up to 130 PowerPC)  Direct matrix Architecture  High data processing bandwidth (up to 128 GB/s)  Data protection with RAID 1, 1+0 (also known as 10 for mainframe), 5, and 6  Storage-based local and remote replication – Through TimeFinder and SRDF software

36. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 36 Direct Matrix Architecture

37. © 2009 EMC Corporation. All rights reserved. Intelligent Storage System - 37 Check Your Knowledge  What are the parts of an Intelligent Storage System?  What are the differences between a high-end and midrange storage array?  What is the difference between a read cache hit and a read cache miss?  What is the difference between Least Recently Used and Most Recently Used algorithms?  What is the difference between Write-through and Write- back cache?