What do you understand by RAID? Explain RAID Level 4 and Level5?
RAID - It is stands for Redundant Array of Inexpensive Disks (as named by the inventor), or alternatively Redundant Array of Independent Disks (a less relative name, and therefore now the commonly accepted one) - is a technology which employs the simultaneous use of two or more hard disk drives to achieve greater stages of performance, reliability, and/or larger data volume sizes.
RAID Level 4: In this setup, files can be distributed among multiple disks. Each disk operates independently that permits I/O requests to be performed in parallel, by data transfer speeds can suffer due to the kind of parity. The error detection is achieved through dedicated parity and is stored within a separate, single disk unit.
RAID Level 5: Distributed parity needs all drives but one to be present to operate; drive failure needs replacement, but the array is not destroyed through a single drive failure. Upon drive failure, any subsequent reads can be computed from the distributed parity such in which the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data in which was on the failed drive is rebuilt onto a replacement drive