© 2009 emc corporation. all rights reserved. storage system environment module 1.2

© 2009 EMC Corporation. All rights reserved.

Storage System EnvironmentStorage System Environment

Module 1.2

© 2009 EMC Corporation. All rights reserved. Storage System Environment - 2

Storage System Environment

Upon completion of this module, you will be able to:

List components of storage system environment– Host, connectivity and storage

List physical and logical components of hosts

Describe key connectivity options

Describe the physical disk structure

Discuss factors affecting disk drive performance


Lesson: Components of Storage System Environment

Upon completion of this lesson, you will be able to:

Describe the three components of storage system environment– Host, Connectivity and Storage

Detail Host physical and logical components

Describe interface protocol– PCI, IDE/ATA and SCSI

Describe storage options– Tape, optical and disk drives


Host

Applications runs on hosts

Hosts can range from simple laptops to complex server clusters

Physical components of host– CPU

– Storage Disk device and internal memory

– I/O device Host to host communications

Network Interface Card (NIC)

Host to storage device communications

Host Bus Adapter (HBA)

LaptopServer

Mainframe

Group of Servers

LAN


Host: Logical Components

Host

DBMS

HBA HBA HBA

Applications

Volume Manager

Operating System

File System

Device Drivers


Logical Components of the Host

Application – Interface between user and the host

– Three-tiered architecture Application UI, computing logic and underlying databases

– Application data access can be classifies as: Block-level access: Data stored and retrieved in blocks, specifying the

LBA File-level access: Data stored and retrieved by specifying the name and

path of files

Operating system– Resides between the applications and the hardware

– Controls the environment


Logical Components of the Host (Cont)

Device Drivers– Enables operating system to recognize the device

– Provides API to access and control devices

– Hardware dependent and operating system specific

File System– File is a collection of related records or data stored as a unit

– File system is hierarchical structure of files Examples: FAT 32, NTFS, UNIX FS and EXT2/3


File System: Metadata Examples

UNIX (UFS)

File type and permissions

Number of links

Owner and group IDs

Number of bytes in the file

Last file access

Last file modification

Windows (NTFS)

Time stamp and link count

File name

Access rights

File data

Index information

Volume information


File Systems: Journaling and Logging

Improves data integrity and system restart time over non-journaling file systems.

Uses a separate area called a log or journal.– May hold all data to be written

– May hold only metadata

Disadvantage - slower than other file systems.– Each file system update requires at least 1 extra write – to the

log


Logical Components of the Host: LVM Responsible for creating and controlling

host level logical storage– Physical view of storage is converted to a

logical view by mapping– Logical data blocks are mapped to physical

data blocks

Usually offered as part of the operating system or as third party host software

LVM Components:– Physical Volumes– Volume Groups– Logical Volumes

Physical Storage

Logical Storage

LVM


Volume Groups One or more Physical Volumes

form a Volume Group

LVM manages Volume Groups as a single entity

Physical Volumes can be added and removed from a Volume Group as necessary

Physical Volumes are typically divided into contiguous equal-sized disk blocks

A host will always have at least one disk group for the Operating System– Application and Operating

System data maintained in separate volume groups

Logical Disk Block

Volume Group

Physical Disk Block

Physical Volume 1 Physical Volume 2 Physical Volume 3

Logical Volume

Logical Volume


LVM Example: Partitioning and Concatenation

Partitioning Concatenation

Logical Volume

Physical Volume

Servers


LVM Example

A Windows XP system with two physical hard disks.

Physical DiskPartition Filesystem Drive Letter

Hard Disk 1 Partition 1 NTFS C:Partition 2 FAT32 D:

Hard Disk 2 Partition 1 FAT32 E:

"C:", "D:", and "E:" are volumes. Hard Disk 1 and Hard Disk 2 are physical disks. Any of these can be called a "drive".


How Files are Moved to and from Storage

1 2 3

456

Consisting of Mapped by LVM to

Teacher (User)Course File(s) File System Files

File System Blocks

LVM Logical Extents

Disk Physical ExtentsDisk Sectors

Configures/Manages

Residing in

Reside in Mapped by a file system to

Managed by disk storage subsystem


Connectivity

Interconnection between hosts or between a host and any storage devices

Physical Components of Connectivity are:– Bus, port and cable

CPU HBA

Port

CableBUS

Disk


Bus Technology

Serial

Serial Bi-directional

Parallel


Bus Technology

System Bus – connects CPU to Memory

Local (I/O) Bus – carries data to/from peripheral devices.

Bus width measured in bits

Bus speed measured in MHz

Throughput measured in MB/S


Connectivity Protocol

Protocol = a defined format for communication between sending and receiving devices

– Tightly connected entities such as central processor to RAM, or storage buffers to controllers (example PCI)

– Directly attached entities connected at moderate distances such as host to storage (example IDE/ATA)

– Network connected entities such as networked hosts, NAS or SAN (example SCSI or FC)

Tightly ConnectedEntities

DirectlyAttachedEntities

Network Connected

Entities


Popular Connectivity Options: PCI

PCI is used for local bus system within a computer

It is an interconnection between microprocessor and attached devices

Has Plug and Play functionality

PCI is 32/64 bit

Throughput is 133 MB/sec

PCI Express – Enhanced version of PCI bus with higher throughput and clock

speed


PCI


Popular Connectivity Options: IDE/ATA

Integrated Device Electronics (IDE) / Advanced Technology Attachment (ATA)– Most popular interface used with modern hard disks

– Good performance at low cost

– Inexpensive storage interconnect

– Used for internal connectivity

Serial Advanced Technology Attachment (SATA)– Serial version of the IDE /ATA specification

– Hot-pluggable

– Enhanced version of bus provides upto 6Gb/s (revision 3.0)


PATA


SATA


Popular Connectivity Options: SCSI

Parallel SCSI (Small computer system interface)– Most popular hard disk interface for servers

– Higher cost than IDE/ATA

– Supports multiple simultaneous data access

– Used primarily in “higher end” environments

– SCSI Ultra provides data transfer speeds of 320 MB/s

Serial SCSI– Supports data transfer rate of 3 Gb/s (SAS 300)


SCSI-Bus Interface Connector


SCSI - Pros and Cons

Pros:– Fast transfer speeds, up to 320

megabytes per second

– Reliable, durable components

– Can connect many devices with a single bus, more than just HDs

– SCSI host cards can be put in almost any system

– Full backwards compatibility

Cons:– Configuration and setup

specific to one computer

– Unlike IDE, few BIOS support the standard

– Overwhelming number of variations in the standard, hardware, and connectors

– No common software interfaces and protocol


Comparison IDE/ATA vs SCSI

Feature IDE/ATA SCSI

Connectivity Market Internal Storage Internal and External Storage

Speed (MB/sec) 100/133/150 320

Hot Pluggable No Yes

Expandability Easier to set up Very good but veryexpensive to set up

Cost/Performance Good High cost/Fasttransfer speed


Storage: Medias and Options

Magnetic Tape– Low cost solution for long term data storage– Limitations

Sequential data access, Single application access at a time, Physical wear and tear and Storage/retrieval overheads

Optical Disks– Popularly used as distribution medium in small, single-user

computing environments– Write once and read many (WORM): CD-ROM, DVD-ROM– Limited in capacity and speed

Disk Drive– Most popular storage medium with large storage capacity– Random read/write access

Ideal for performance intensive online application


Lesson Summary

Key points covered in this lesson:

Host components– Physical and Logical

Connectivity options– PCI, IDE/ATA, SCSI

Storage options– Tape, optical and disk drive


Lesson: Disk Drive

Upon completion of this lesson, you will be able to:

List and discuss various disk drive components– Platter, spindle, read/write head and actuator arm assembly

Discuss disk drive geometry

Describe CHS and LBA addressing scheme

Disk drive performance– Seek time, rotational latency and transfer rate

Law’s governing disk drive performance

Enterprise flash drive


Disk Drive Components

Interface

Controller

Power Connector

HDA


Physical Disk Structure

Sector

Track

Platter

SectorTrack

Cylinder

Spindle


Logical Block Addressing

Physical Address= CHS

Cylinder 2

Head 0

Sector 10

Block 48

Block 16

Block 32

Logical Block Address= Block#

Block 0

Block 8

(Upper Surface)

(Lower Surface)


Platter Geometry and Zoned-Bit Recording

Platter Without Zones

Sector

Track

Platter With Zones


Disk Drive Performance

Electromechanical device– Impacts the overall performance of the storage system

Disk Service Time– Time taken by a disk to complete an I/O request

Seek Time Rotational Latency Data Transfer Rate


Disk Drive Performance: Seek Time

Time taken to position the read/write head

Lower the seek time, the faster the I/O operation

Seek time specifications include:– Full stroke

– Average

– Track-to-track


Disk Drive Performance: Rotational Speed/Latency

The time taken by platter to rotate and position the data under the R/W head

Depends on the rotation speed of the spindle

Average rotational latency – One-half of the time taken for a full

rotation

– Appx. 5.5 ms for 5400-rpm drive

– Appx. 2.0 ms for 15000-rpm drive


Disk Drive Performance: Data Transfer Rate

Average amount of data per unit time

Internal Transfer Rate– Speed at which data moves from a track to disk internal buffer

External Transfer Rate– The advertised speed of the interface

InterfaceInterface BufferBufferHBAHBA

Disk Drive

Internal transfer rate measured here

External transfer rate measured here

Head Disk AssemblyHead Disk Assembly


SATA vs SAS drives in 3.5-in form factor in 2006

Power consumed by the disk motor:Power Diameter4.6 ×RPM2.8 × Number of platters

Power Consumption


Fundamental Laws Governing Disk Performance

Little’s Law– Describes the relationship between the number of requests in a queue and the

response time.

– N = a × R “N” is the total number of requests in the system “a” is the arrival rate “R” is the average response time

Utilization law– Defines the I/O controller utilization

– U = a × RS

“U” is the I/O controller utilization “RS“ is the service time

126 5 4 3I/O

ControllerProcessed I/O Request

ArrivalI/O Queue


Utilization vs. Response time

Consider a disk I/O system in which an I/O request arrives at a rate of 100 I/Os per second. The service time, RS, is 4 ms. – Utilization of I/O controller (U = a × Rs) – Total response time (R=Rs /1–U) – Time spent by a request in a queue Rq = Rs U /(1–U) – Average queue size = U2 / (1–U)

Calculate the same with service time is doubled

0% 100%Utilization

Knee of curve: disks at

about 70% utilization

Low Queue Size

70%


Application Requirements and Disk Performance

Exercise:

Consider an application that requires 1TB of storage capacity and performs 4900 IOPS – Application I/O size is 4KB– As it is business critical application, response time must be

within acceptable range

Specification of available disk drive:– Drive capacity = 73 GB – 15000 RPM– 5 ms average seek time– 40 MB/sec transfer rate

Calculate the number of disks required?


Solution

Calculate time required to perform one I/O Seek time + (rotational delay)/speed in RPM + (block size/transfer rate)

Therefore, 5 ms + 0.5 /15000 + 4K/40MB = 7.1 msec

Calculate max. number of IOPS a disk can perform– 1 / 7.1 ms = 140 IOPS

For acceptable response time disk controller utilization must be less than 70%– Therefore, 140 X 0.7 = 98 IOPS

To meet application – Performance requirement we need 4900/98 i.e. 50 disk– Capacity requirement we need 1TB/ 73 GB i.e. 14 disk

Disk required = max (capacity, performance)


Enterprise Flash Drives: A New Generation Drives

Conventional disk drive

Mechanical Delay associated with conventional drive

– Seek time

– Rotational latency

More power consumption due to mechanical operations

Low Mean Time Between Failure

Enterprise flash drive

Highest possible throughput per drive– No Spinning magnetic media– No Mechanical movement which

causes seek and latency– Solid State enables consistent I/O

performance

Very low latency per I/O

Energy efficient storage design– Lower power requirement per GB of

storage

– Lower power requirement per IOPS


Enterprise Flash Drives – Overview

Drive is based on Flash Solid State memory technology– High performance and low latency

– Non volatile memory

– Uses single layer cell (SLC) or Multi Level cell (MLC) to store data

Enterprise Flash Drives use a 4Gb FC interface


Enterprise Flash Drives – Benefits

Faster performance– Up to 30 times greater IOPS

(benchmarked)

– Typical applications: 8 – 12X

– Less than 1 millisecond service time

More energy efficient– 38 percent less per terabyte

– 98 percent less per IO

Better reliability– No moving parts

– Faster RAID rebuilds

IO per secondR

esp

on

se T

ime

1 Flash drive

1@15K FibreChannel drive

10@15K Fibre Channeldrives

30@15KFibre

Channel drives


Enterprise Flash Drives – “Tier-0” Application

Position Enterprise Flash Drives as the high-performance option in demanding environments– Low latency applications, also known as “Tier-0”

applications

Standard form-factor and capacity design allows for easier integration

High performance, low power for a “Green” initiative

Target Customer/Market Segments:– High performance solutions coupled with low power– Specifically target Oracle database customers initially– Financial trading– OLTP databases


Lesson Summary

Key points covered in this lesson:

Disk drive components and geometry

Disk drive addressing scheme

Disk drive performance

Convention drive Vs Enterprise Flash Drives

Enterprise Flash Drives for high performance and low power storage solution


Module Summary

Key points covered in this module:

Storage system environment components:– Host, connectivity and storage

Physical disk structure and addressing

Factors affecting disk performance

Flash drives benefits


Check Your Knowledge

What are some examples of hosts?

What are the physical and logical components of a host?

What are the common connectivity protocols used in computing environments?

What is the difference between seek time and rotational latency?

What is the difference between internal and external data transfer rates?

© 2009 emc corporation. all rights reserved. storage system environment module 1.2

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file system device drivers

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