WHAT IS RAID?Christopher J DutraSeton Hall University

What is RAID?

RAID stands for a redundant array of inexpensive disks. (sometimes inexpensive is replaced with independent).

RAID is a storage scheme in which many hard disks are bundled together in an “array” to act as one disk.

Developed by UC-Berkley scientists in 1987.

Benefits

Higher Data Security Fault Tolerance Improved Availability Increased Storage Capacity with

Integrated Disks Improved Performance

Higher Data Security

A RAID can still operate if a single disk inside the RAID fails.

Also would not require any data to be restored from a backup disk.

Primary reason why people purchase RAIDs.

Tradeoffs

There are three components to RAID servers to consider when purchasing: Speed : overall performance, capacity Reliability : amount of fault tolerance

expected Cost : amount you are willing to spend.

General rule of thumb is “pick two.”

Also, for complex raid servers, hours of setup and maintenance is expected.

RAID Limitations

RAID won’t protect data loss against: viruses power surges multiple hardware failures (sometimes) sabotage

IMPORTANT : MAINTAIN CURRENT BACKUPS.

RAID LEVELS

RAID 0 – Files are broken into “stripes” of a user-defined size of the array, and stripes are sent to each disk in the array.

It has worse reliability than a hard disk, used for greater performance. Cheap to implement, but not very reliable. Must maintain current backups should RAID 0 fail.

Example of RAID 0

This is a four-disk, 16 KB stripe size RAID 0 array.

Source: www.pcguide.com

RAID 1

RAID 1– has its data duplicated on another hard disk. That way, should one of the hard drives fail, the other is operable until the faulty drive is replaced.

Also, a technique called duplexing provides fault tolerance against either hard drive or the RAID controller.

Performance is compromised slightly.

RAID 5

RAID level 5—one of the most popular RAID configurations, RAID 5 stripes both data and parity information across three or more drives.

Fault tolerance is maintained by ensuring that the parity information for any given block of data is placed on a drive separate from those used to store the data itself. (pcguide.com)

Example of RAID 5

This is a four-disk, 16 KB stripe size RAID 5 array.

Source: www.pcguide.com

Why buy RAID?

Business servers – provides data protection (especially good for when loss of data could cripple a business)

Workstations – for graphical design, video editing, a RAID system would improve the performance of high-overhead programs (such as 3dStudio Max).

Regular PC’s –do not necessarily need RAID, could help in the future though (as video games and other applications become more costly in resources).