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            Some Basic Understanding of RAID


RAID stands for Redundant  Aarray of Inexpensive Disks. The technology  was introduced  in  1987 by University of California, Berkeley. During  that time, the disk capacity was just barely more than 20 MB or so. It was difficult to store and process huge data. RAID came in  handy  as it could now combine a number of hard disks to meet the  desire capacity. It also had the  additional advantages of improving performance and introduce fault tolerance against single disk failure. So it appeared to be  a perfect solution for high end  computing.

RAID can be implemented on dedicated hardware controller, commonly known as RAID controller. This is called hardware RAID. Conversely, if we leave it to the operating system to handle, we end up with software RAID.

Below shows some comparision between these two.
Hardware Raid Software RAID Remarks
Use hardware such as RAID controller.
Operating system to handle. Powerful modern CPU has diminished the gap betweeen hardware and software RAID
Cost is higher but more efficient Cheaper but take up host CPU time, hence slower performance. With modern CPU, such effect may be negligible now.
Modern LInux OS handles software raid very efficiently with even online rebuild
Selection of disk types  and connection interface must comply with RAID Controller
As long as the bunch of disks are conencted to the computer under running OS Modern Linux could support software RAID even for USB drives.
Moving RAID volume to different server is less portable
RAID volume can be eaily moved to different server with same OS Moving disks to even same controller in different servers may not restore the RAID volume.
Easier to configure RAID volume from built-in BIOS of controller
May need some good technical skills to configure the RAID volume Modern OS has friendly GUI to facilitate configuration of RAID
RAID5 Array
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Modern implementation of RAID server, be it hardware- or software-raid, may come in the forms of Network-Attached Storage, Direct-Attached storage and Storage Area Network.