If you, like me, work in Information Technology with a lot of computers and technology you'll come into contact with file servers and RAID technology. Computer support experts need to provide
RAID support and RAID data recovery services to their clients. Nearly all computer servers run a level of RAID, and RAID is simply a means of data storage that uses more than 1 hard drive. As
there is so much data stored by to hard drive these days, organisations and even small companies rely on RAIDed file servers which hold all their data on several hard drives.
RAID is available at a variety of 'levels', the most common being RAID 5, RAID 0 and RAID 1, but others such as RAID 6, RAID 10 and RAID 50 exist too. I once remember that we tackled a data recovery from a RAID 4 system too in the distant past, that was interesting and we recovered the files back for the client as well. For a more indepth comentary on RAID, visit this Wikipedia link.
A RAID will typically consist of several hard drives whose capacity is combined to make one large storage volume. So, an example RAID 5 array may contain 10 2TB hard drives which will give an overall data storage capacity of 18TB. Large RAID arrays are made by Dell, HP and IBM, it's possible to customer build a RAID server array, and with the advent of NAS technology many business use NAS hard drives as inexpensive RAID 5 file servers. Home users will often use RAID 1 NAS storage, companies and people who work with applications that need a lot of data transfer speed (eg. videographers) will use RAID 0, and companies and organisations RAID 5.
Recovering files and folders from a RAID array that has crashed is a difficult job, and should not be tackled by people without experience. My own personal knowledge is such that I recommend if you need a RAID data recovery you contact a reliable RAID data recovery company like Data Clinic (http://www.dataclinic.co.uk/hard-disk-raid-recovery/) who will apply an expert diagnosis and recovery procedure to the faulty RAID servers. Companies like Data Clinic have a very high success rate at recovering RAID data and should be used whenever file or data access on a RAID is lost.