RAID 5 NAS server

RAID 5

— the operation of these arrays is based on the use of service information in the form of checksums. Checksums (CS) describe the difference between one part of the file and others; due to this, you can easily restore the original data even if one of the fragments is irretrievably lost. When writing to RAID 5, the functions of disks are distributed as follows: fragments of the main data are written to all but one, and the CS derived for these fragments is written to the rest. At the same time, for each “portion” of information, the disk on which the CS is recorded changes. Accordingly, all media in a RAID 5 array contains both the main data portions and the checksums. This ensures the reliability of storage — even with a complete failure of one drive, information can be restored in full. At the same time, the redundancy is very small, because only one disk "falls out" of the useful volume. The disadvantages of RAID 5 are relatively low performance, as well as a sharp decrease in reliability in the event of a failure of one of the media. The minimum disks for such an array is three.