SAN: Storage Area Network

•Block Oriented Access To Data

•Unique Writer

•I/O Protocol: SCSI, HIPPI, IPI

•“Back-end” Network

NAS and SAN

•NAS – Network Attached Storage

–File-oriented access
–Multiple Clients, Shared Access to Data

•SAN – Storage Area Network
–Block-oriented access
–Single Server, Exclusive Access to Data

NAS: Network Attached Storage

•File Objects and Filesystems

–OS Dependent
–OS Access & Authentication

•Possible Multiple Writers
–Require locking protocols

•Network Protocol: i.e., IP

•“Front-end” Network

How Hardware RAID Works ?

When any drive under RAID fails it informs the same through LED indication (or ‘Beep’), as well it can provide information over LAN (if supported and configured). At the same time the RAID CPU sets the state of other disks to ‘0’ (virtually, meaning those are available with data) and the failed slot to ‘1’. The administrator is supposed to replace the failed disk with a new one. On ‘snooping’ the new disk, it assigns the logic ‘1’ for the new disk (doing an ‘XOR’ function of all logical state of all other disks). Then the RAID logic starts ‘Rebuilding’ the data to the drive having logical state ‘1’ getting data from all logical state ‘0’ drives.
This kind of implementation is called ‘Hardware XOR’.

Types Of RAID

Basically there are two types of RAID implementation :
• Software RAID :
RAID functionality is provided by the OS itself.
OS overhead is high.
System Performance is slow.
Low priced solution.
• Hardware RAID :
Separate hardware is there to provide RAID functionality.
Very low OS overhead.
High performance.
Implementation cost higher.


Software RAID A Bit In Detail

•Software RAID can be implemented from NOS like WinNT, Win2K , SCO OSR ,Linux etc.

• In this type of implementation all RAID functionalities are taken care by the host CPU which ultimately tax upon the CPUs ability to perform other computations.
This is pretty low cost solution. Practically customer does not need to buy anything (hardware or software) extra (except for the required HDD). The basic OS can do this functionality

•Software RAID is “Pseudo RAID”. It does not support all basic RAID functionalities & levels.

• It does not require any extra hardware and even can work over IDE interface.

• This is not an OS independent solution. Thus OS structure and limitations plays a major role in its capability.

Software RAID is NOT Valid solution for high Mission critical and high performance Servers


Hardware RAID In Detail

•Hardware RAID requires a RAID controller.

•In this type of implementation all RAID functionalities are taken care by the RAID CPU which offloads the host CPUs transaction with HDDs to a great extent (nearly 90%).

•This is a priced solution…..what I mean, one need to buy a RAID card extra to have better fault- tolerance, availability and performance of the Server system. Better the features, higher the price is ...

•Hardware RAID is “Real RAID”. It supports all basic RAID functionalities and levels.

•Performance is very high, since RAID CPU offloads host CPU.

•This is an OS independent solution. Thus OS structure and limitations does not play any role in its capability.

•It gives a connectivity benefits of SCSI as well.

•More robust fault-tolerant when compared with Software RAID.


Hardware RAID is THE SOLUTION for Mission critical and High performance servers.

RAID Types

•RAID 0
–Stripe with No Parity
•RAID 1
–Mirror two or more disks
•RAID 1+0
–Mirrors & Stripe
•RAID 3
– Dedicated Parity Drive
•RAID 5
–Parity striped across multiple drives

RAID Levels

RAID 0

• Disk Striping
• No Fault Tolerance
• 100% of Disk capacity available
• Performance is very high
• Minimum 2 disks required

RAID 1

• Disk Mirroring
• Highest Level Of Fault Tolerance
• 50% of Used Disk capacity available
• Performance is high
• Minimum 2 disks required

RAID 3

• Disk Stripping with dedicated parity
• High Level Of Fault Tolerance
• Capacity = [(n-1)/n]*100%
• Performance is very high
• Minimum 3 disks required

RAID 5

• Disk Stripping with distributed parity
• High Level Of Fault Tolerance
• Capacity = [(n-1)/n]*100%
• Performance is very high
• Minimum 3 disks required

RAID 10

• Mirroring over stripped Disk set
• High Level Of Fault Tolerance
• Capacity = 50% of disk used
• Performance is very high
• Minimum 4 disks required
• Used in mission critical environment, where price sits at lower bench than
  performance and availability factors.

RAID Function – Pro & Con

•Striping
–Pro: Increases Spindle Count for Increased Thruput
–Con: Does not provide redundancy

•Mirroring
–Pro: Provides Redundancy without Parity Calculation
–Con: Requires at least 100% disk resource overhead

•Parity Calculation
–Pro: Cuts Disk Resource Overhead to 1/N
–Con: Parity calculation is expensive

RAID Functions

•Striping
–Write consecutive logical byte/blocks on consecutive physical disks
•Mirroring
–Write the same block on two or more physical disks
•Parity Calculation
–Given N disks, N-1 consecutive blocks are data blocks, Nth block is for parity
–The Data Block(s) and Parity Block are written
–Destroy two or more blocks – reconstruction is not possible

Raid

Why Raid

•Redundant Array of Inexpensive Disks
•Combine multiple disks into a single virtual device
•How this is implemented determines different strengths
–Storage Capacity
–Speed
•Fast Read or Fast Write
–Resilience in the face of device failure

Basic of Data Storage

TYPES OF STORAGES
Embedded
–Internal Disks within the System Chassis
Directly Attached
–External Chassis of Disks connected to a Server via a Cable
Directly Attached Shared
–External Chassis connected to more than one Server via a Cable
Networked Storage
–NAS
–SAN
–CAS