What is RAID? - a basic explanation

We often get asked “What is a RAID system?” Very often the person posing the question has no idea and coupled with the fact that the use of RAID is becoming increasing common amongst small businesses and home users we felt it time that an explanation was given along with the problems that are often associated when recovering data from a RAID or server system.

The term RAID is a standardised expression for Redundant Array of Inexpensive (or Independent) Disks. In short RAID is a data storage system created with more than one disk in the system so that data is spanned across more than the one disk. However the whole system combines to give the impression that you are simply using a single hard disk or storage unit. The main purpose of this is to add to data security and prevent data loss, as of course no one single method of storage is deemed to be completely 100% reliable.

There are many different types of RAID Array but we will focus on the three main systems currently in use that we come across when asked to recover data from RAID storage systems.

RAID 0

This is where an array of usually 2, but it can contain more, disks has data striped across it simultaneously. This means that the data is written across the two disks allowing for greater speed when accessing and writing data to the system but there is no inbuilt redundancy should one of the disks fail. Therefore you are always advised to ensure an adequate backup of a RAID 0 is maintained which would then pose the question of why are you using a RAID 0 anyway? It is rare that both of the disks will fail at the same time unless a portable storage unit is dropped but very often one of the disks in the array will fail, perhaps bad sectors have developed, and this is enough to make the data inaccessible. With a RAID 0 BOTH disks need to be present and full working in order for data access to be possible. An standard example of a RAID 0 system is pictured to the right - a LaCie Big Disk (image courtesy of LaCie)

RAID 1

Is often referred to a “mirroring” and this is where a two drive system is employed where the data contained on drive A is replicated (mirrored) on drive B. This a great way of ensuring that should one drive fail you have a complete backup of the data.

RAID 5

This is possibly the most common form of RAID that we are asked to recover data from. A system of three or more disks is employed with a single disk redundancy inbuilt to the overall system. This means that one of the disks in the system can fail and the you will suffer no data loss and you simply have to insert a replacement disk to restore the system to full order. The most common form of RAID 5 is the 4 disk system. Should more than one disk fail then the array will suffer from data loss but again it is rare for more than one disk to fail at the same time.

For full information of RAID 5 see our dedicated website Expidata

Other examples include RAID 2,3,6,10 & 50 but these are not common in the general data recovery market for small businesses and home users.

If you have a RAID system and have lost from it or any other general questions regarding this article then please don’t hesitate to contact the team at VenSys Limited. We recommend that should your RAID system fail do not attempt to either recover the data or reinitialise the array yourself and give us a call for a no obligation chat about the situation