WHAT IS RAID? Christopher J Dutra Seton 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:

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:

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).