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Points IDE Drive SATA Drive SCSI Drive
Abbreviations Integrated Drive Electronics Serial Advanced Technology Attachment Small Computer System Interface
Speed 8.3 MBps 150 Mbps 3 Gbps
Used in same Environment NO YES NO
Cable Size Large Small Small
Data Transferring Parallel Serial Serial
Raid Technology
Raid Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers. RAID allows you to store the same data redundantly (in multiple paces) in a balanced way to improve overall performance.
There are number of different RAID levels
Level 0: Striped Disk Array without Fault Tolerance Provides data striping (spreading out blocks of each file across multiple disk drives) but no redundancy. This improves performance but does not deliver fault tolerance. If one drive fails then all data in the array is lost.
Level 1 Mirroring and Duplexing : Provides disk mirroring. Level 1 provides twice the read transaction rate of single disks and the same write transaction rate as single disks.
Level 2 Error-Correcting Coding Not a typical implementation and rarely used, Level 2 stripes data at the bit level rather than the block level.
Level 3 Bit Interleaved Parity: Provides byte-level striping with a dedicated parity disk. Level 3, which cannot service simultaneous multiple requests, also is rarely used.
Level 4 -- Dedicated Parity Drive A commonly used implementation of RAID, Level 4 provides block-level striping (like Level 0) with a parity disk. If a data disk fails, the parity data is used to create a replacement disk. A disadvantage to Level 4 is that the parity disk can create write bottlenecks.
Level 5 Block Interleaved Distributed Parity Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.
Level 6 Independent Data Disks with Double Parity: Provides block-level striping with parity data distributed across all disks.
Level 0+1 A Mirror of Stripes Not one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1 mirror is created over them. Used for both replicating and sharing data among disks.
Level 10 A Stripe of Mirrors Not one of the original RAID levels, multiple RAID 1 mirrors are created, and a RAID 0 stripe is created over these.
Level 7 A trademark of Storage Computer Corporation that adds caching to Levels 3 or 4.
Raid Level We Supported
Points RAID 0 RAID 1
Known As Stripping Mirroring
Hard disk Minimum one Exactly two
Performance Very good Comparatively good
Data Stored In different hard disk In Both Hard disk
Advantage You can use large volume by attaching number of drives Though using two drives only one hard disk space
Disadvantage When drive fails data will be lost Only we can use one hard disk as we have attached two
Disk array controller
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A disk array controller is a device which manages the physical disk drives and presents them to the computer as logical units. It almost always implements hardware RAID, thus it is sometimes referred to as RAID controller. It also often provides additional disk cache.
A disk array controller name is often improperly shortened to a disk controller. The two should not be confused as they provide very different functionality.
Contents
[hide]
• 1 Front-end and back-end side
• 2 Enterprise controllers
• 3 Simple controllers
o 3.1 History
• 4 References
Front-end and back-end side
Disk array controller provides front-end interfaces and back-end interfaces.
• Back-end interface communicates with controlled disks. Hence protocol is usually ATA (a.k.a. PATA; incorrectly called IDE), SATA, SCSI, FC or SAS.
• Front-end interface communicates with a computer's host adapter (HBA, Host Bus Adapter) and uses:
o one of ATA, SATA, SCSI, FC; these are popular protocols used by disks, so by using one of them a controller may transparently emulate a disk for a computer
o somewhat less popular protocol dedicated for a specific solution: FICON/ESCON, iSCSI, HyperSCSI, ATA over Ethernet or InfiniBand
A single controller may use different protocols for back-end and for front-end communication. Many enterprise controllers use FC on front-end and SATA on back-end.
[edit] Enterprise controllers
Main article: Disk array
In a modern enterprise architecture disk array controllers are parts of physically independent enclosures, such as disk arrays placed in a storage area network (SAN) or network-attached storage (NAS) servers.
Those external disk arrays are usually purchased as an integrated subsystem of RAID controllers, disk drives, power supplies, and management software. It is up to controllers to provide advanced functionality (various vendors name these differently):
• automatic failover to another controller (transparent to computers transmitting data)
• long-running operations performed without downtime
o forming a new RAID set
o reconstructing degraded RAID set (after a disk failure)
o adding a disk to online RAID set
o removing a disk from a RAID set (rare functionality)
o partitioning a RAID set to separate volumes/LUNs
• snapshots
• Business Continuance Volumes (BCV)
• replication with a remote controller....
Simple controllers
Promise Technology ATA RAID controller
A simple disk array controller may be fit inside a computer, either as a PCI expansion card or just built into the motherboard. Such controller usually provides host bus adapter (HBA) functionality itself to save physical space. Hence it is sometimes called a RAID adapter.
More recently (February 2007) Intel has started integrating their own Matrix RAID controller in their more upmarket motherboards giving control over 4 devices and an additional 2 SATA connectors, totalling to 6 SATA connections (3Gbit/s each). For backward compatibility one IDE connector enabling to connect 2 ATA devices (100 Mbit/s) is also present.
[edit] History
While hardware RAID controllers were available for a long time, they always required expensive SCSI hard drives and aimed at the server and high-end computing market. SCSI technology advantages include allowing up to 15 devices on one bus, independent data transfers, hot-swapping, much higher MTBF.
Around 1997, with the introduction of ATAPI-4 (and thus the Ultra-DMA-Mode 0, which enabled fast data transfers with less CPU utilization) the first ATA RAID controllers were introduced as PCI expansion cards. Those RAID systems made their way to the consumer market, where the users wanted the fault-tolerance of RAID without investing in expensive SCSI drives.
ATA drives make it possible to build RAID systems at lower cost than with SCSI, but most ATA RAID controllers lack a dedicated buffer or high-performance XOR hardware for parity calculation. As a result, ATA RAID performs relatively poorly compared to most SCSI RAID controllers. Additionally, data safety suffers if there is no battery backup to finish writes interrupted by a power outage.
RAID Controllers and RAID Controller cards
Definition: A RAID controller is a hardware device responsible for managing physical drives in a system and presenting them to the computer as logical units.
The setting up of RAID 0 and RAID 1 can be done either via software or hardware. Some operating systems allow you to setup RAID in the software itself. A better option is to have a dedicated piece of hardware controlling the RAID functions. A guide to software RAID in Linux.
RAID controller chips are often imbedded in the motherboard. They also come in the form of a PCI expansion cards.
Hardware RAID You need to ensure that the RAID controller card is designed for the type of hard disks you are using. A RAID controller card designed for use with IDE hard disks will not take SCSI hard disks. A controller designed to provide just RAID 0 functions will not allow you to set up a fault tolerant array.
The big names in the RAID controller business are Adaptec, Highpoint, Intel and Promise. Highpoint and Promise supply most of the RAID chips that are imbedded in both single CPU and dual processor motherboards. They also make the RAID controller cards which are sold on their own. Intel uses it's RAID controller chips in motherboards they produce, Adaptec is mainly known for it's SCSI based products including SCSI cards and SCSI RAID controller cards. Many of the manufacturers also build specialist RAID controller cards for use in "non-standard" situations, eg low profile RAID controller cards for use in restricted spaces like 2 U server cases etc. You can even get RAID for use with newer technologies like SATA. Companies like 3Ware manufacture SATA RAID controller cards.
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