Storage System Environment

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Storage System EnvironmentStorage System Environment

Chapter 2

Section 1 : Storage System


Chapter Objectives

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

o List components of storage system environmento Host, connectivity and storage

o List physical and logical components of hosts

o Describe key connectivity options

o Describe the physical disk structure

o Discuss factors affecting disk drive performance


Lesson: Components of Storage System Environment

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

o Describe the three components of storage system environmento Host, Connectivity and Storage

o Detail Host physical and logical components

o Describe interface protocolo PCI, IDE/ATA and SCSI

o Describe storage optionso Tape, optical and disk drives


Hosto Applications runs on hosts

o Hosts can range from simple laptops to complex server clusters

o Physical components of hosto CPUo Storage

o Disk device and internal memory

o I/O deviceo Host to host communications

o Network Interface Card (NIC)o Host to storage device communications

o 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

o Application o Interface between user and the host o Three-tiered architecture

o Application UI, computing logic and underlying databaseso Application data access can be classifies as:

o Block-level access: Data stored and retrieved in blocks, specifying the LBAo File-level access: Data stored and retrieved by specifying the name and path of

files

o Operating systemo Resides between the applications and the hardwareo Controls the environment


Logical Components of the Host: LVMo Responsible for creating and controlling host

level logical storageo Physical view of storage is converted to a

logical view by mappingo Logical data blocks are mapped to physical data

blocks

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

o LVM Components:o Physical Volumeso Volume Groupso Logical Volumes

Physical Storage

Logical Storage

LVM


Volume Groupso One or more Physical Volumes

form a Volume Group

o LVM manages Volume Groups as a single entity

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

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

o A host will always have at least one disk group for the Operating System

o 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


Logical Components of the Host (Cont)

o Device Driverso Enables operating system to recognize the device o Provides API to access and control deviceso Hardware dependent and operating system specific

o File Systemo File is a collection of related records or data stored as a unit o File system is hierarchical structure of files

o Examples: FAT 32, NTFS, UNIX FS and EXT2/3

Additional Task

Research on Blade Server

Technology & File Systems


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

o Interconnection between hosts or between a host and any storage devices

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

CPU HBA

Port

CableBUS

Disk


Connectivity Protocolo Protocol = a defined format for communication between sending and

receiving devices

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

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

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

Tightly ConnectedEntities

DirectlyAttachedEntities

Network Connected

Entities


Popular Connectivity Options: PCI

o PCI is used for local bus system within a computer

o It is an interconnection between microprocessor and attached devices

o Has Plug and Play functionality

o PCI is 32/64 bit

o Throughput is 133 MB/sec

o PCI Express o Enhanced version of PCI bus with higher throughput and clock speed


Popular Connectivity Options: IDE/ATA

o Integrated Device Electronics (IDE) / Advanced Technology Attachment (ATA)o Most popular interface used with modern hard diskso Good performance at low costo Inexpensive storage interconnecto Used for internal connectivity

o Serial Advanced Technology Attachment (SATA)o Serial version of the IDE /ATA specification o Hot-pluggableo Enhanced version of bus provides upto 6Gb/s (revision 3.0)


Popular Connectivity Options: SCSI

o Parallel SCSI (Small computer system interface)o Most popular hard disk interface for serverso Higher cost than IDE/ATAo Supports multiple simultaneous data accesso Used primarily in “higher end” environments o SCSI Ultra provides data transfer speeds of 320 MB/s

o Serial SCSIo Supports data transfer rate of 3 Gb/s (SAS 300)


Storage: Medias and Optionso Magnetic Tape

o Low cost solution for long term data storageo Limitations

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

o Optical Diskso Popularly used as distribution medium in small, single-user computing

environmentso Write once and read many (WORM): CD-ROM, DVD-ROMo Limited in capacity and speed

o Disk Driveo Most popular storage medium with large storage capacityo Random read/write access

o Ideal for performance intensive online application


Lesson Summary

Key points covered in this lesson:

o Host componentso Physical and Logical

o Connectivity optionso PCI, IDE/ATA, SCSI

o Storage optionso Tape, optical and disk drive

Additional Task

Research on various media

technologies & their performance


Lesson: Disk Drive

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

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

o Discuss disk drive geometry

o Describe CHS and LBA addressing scheme

o Disk drive performanceo Seek time, rotational latency and transfer rate

o Law’s governing disk drive performance

o 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)


Disk Drive Performance

o Electromechanical deviceo Impacts the overall performance of the storage system

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

o Seek Timeo Rotational Latency o Data Transfer Rate

Disk service time = Seek time + (rotational delay/speed in RPM)+ (block size/transfer rate)


Disk Drive Performance: Seek Timeo Time taken to position the

read/write head

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

o Seek time specifications include:

o Full strokeo Averageo Track-to-track


Disk Drive Performance: Rotational Speed/Latencyo The time taken by platter to rotate

and position the data under the R/W head

o Depends on the rotation speed of the spindle

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

rotationo Appx. 5.5 ms for 5400-rpm driveo Appx. 2.0 ms for 15000-rpm drive


Disk Drive Performance: Data Transfer Rateo Average amount of data per unit time

o Internal Transfer Rateo Speed at which data moves from a track to disk internal buffer

o External Transfer Rateo 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


Fundamental Laws Governing Disk Performanceo Little’s Law

o Describes the relationship between the number of requests in a queue and the response time.

o N = a × Ro “N” is the total number of requests in the systemo “a” is the arrival rate o “R” is the average response time

o Utilization lawo Defines the I/O controller utilizationo U = a × Rs

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

126 5 4 3I/O

ControllerProcessed I/O Request

ArrivalI/O Queue


Utilization vs. Response time

o 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.

o Utilization of I/O controller (U= a × Rs) o Total response time (R=Rs /1-U)

o Calculate the same with service time is doubled

0% 100%Utilization

Knee of curve: disks at

about 70% utilization

Low Queue Size

70%

Additional Task

Research on Disc Drive Technology


Enterprise Flash Drives: A New Generation DrivesConventional disk drive

o Mechanical Delay associated with conventional drive

o Seek time o Rotational latency

o More power consumption due to mechanical operations

o Low Mean Time Between Failure

Enterprise flash drive

o Highest possible throughput per driveo No Spinning magnetic mediao No Mechanical movement which causes

seek and latencyo Solid State enables consistent I/O

performance

o Very low latency per I/O

o Energy efficient storage designo Lower power requirement per GB of

storageo Lower power requirement per IOPS


Enterprise Flash Drives – Overview

o Drive is based on Flash Solid State memory technologyo High performance and low latency o Non volatile memoryo Uses single layer cell (SLC) or Multi Level cell (MLC) to store data

o Enterprise Flash Drives use a 4Gb FC interface


Enterprise Flash Drives – Benefits

o Faster performanceo Up to 30 times greater IOPS

(benchmarked)o Typical applications: 8 – 12Xo Less than 1 millisecond service

time

o More energy efficiento 38 percent less per terabyteo 98 percent less per IO

o Better reliabilityo No moving partso 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” Applicationo Position Enterprise Flash Drives as the high-performance

option in demanding environmentso Low latency applications, also known as “Tier-0” applications

o Standard form-factor and capacity design allows for easier integration

o High performance, low power for a “Green” initiative

o Target Customer/Market Segments:o High performance solutions coupled with low powero Specifically target Oracle database customers initiallyo Financial tradingo OLTP databases

Additional Task

Research on Flash Drive

Technology


Lesson Summary

Key points covered in this lesson:

o Disk drive components and geometry

o Disk drive addressing scheme

o Disk drive performance

o Convention drive Vs Enterprise Flash Drives

o Enterprise Flash Drives for high performance and low power storage solution


Application Requirements and Disk Performance

Exercise:

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

acceptable range

oSpecification of available disk drive:o Drive capacity = 73 GB o 15000 RPMo 5 ms average seek timeo 40 MB/sec transfer rate

Calculate the number of disks required?


Solutiono 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

o Calculate max. number of IOPS a disk can performo 1 / 7.1 ms = 140 IOPS

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

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

Disk required = max (capacity, performance)


Chapter Summary

Key points covered in this chapter:

o Storage system environment components:o Host, connectivity and storage

o Physical disk structure and addressing

o Factors affecting disk performance

o Flash drives benefits


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Storage System Environment