RAID 5 PCI controllers

RAID 5

— recording format that involves the use of the so-called checksums — service data used for error correction.

RAID 5 array must include at least three drives. And information is written to them in the following way: data fragments are written to all disks, except for one, and the checksum of these fragments is written to the remaining disk. At the same time, the disks on which the checksum is written change every time: for example, in an array of 4 disks, the first three fragments are written to the first, second and third disk, their checksum to the fourth, the second three fragments to the second, third and fourth with a checksum on the first one, etc.

The meaning of the checksum is that it can be used to restore the lost data fragment if necessary. Thus, RAID 5 arrays have good fault tolerance with relatively low redundancy: the total array size is equal to the sum of the capacities of all disks minus the capacity of one disk, and when one of the drives fails, lost data is restored using checksums. On the other hand, the performance of such arrays is lower than individual drives due to additional operations for calculating checksums. And when two or more drives fail, the entire array becomes unavailable.