Redundant Array of Independent Disks, or RAID, is a method of keeping content on a number of hard disk drives at the same time. A RAID could be software or hardware based on the HDDs that are used - physical or logical ones, still what’s common between them is the fact that they all function as just one single unit where info is stored. The main advantage of using a RAID is redundancy as the info on all drives will be exactly the same all the time, so even in case some drive fails for some reason, the info will still be available on the rest of the drives. The overall performance is also better as the reading and writing processes could be split between a number of drives, so a single one will not be overloaded. There are different types of RAIDs where the capabilities and fault tolerance could differ based on the specific setup - whether information is written on all of the drives real-time or it is written on a single drive and after that mirrored on another, what number of drives are used for the RAID, etc.
RAID in Hosting
The state-of-the-art cloud web hosting platform where all hosting accounts are created employs fast SSD drives instead of the traditional HDDs, and they function in RAID-Z. With this configuration, multiple hard disk drives function together and at least 1 is a dedicated parity disk. Put simply, when data is written on the other drives, it's copied on the parity one adding an extra bit. This is done for redundancy as even if some drive fails or falls out of the RAID for some reason, the data can be rebuilt and verified using the parity disk and the data recorded on the other ones, therefore not a single thing will be lost and there won't be any service disorders. This is another level of security for your info together with the top-notch ZFS file system which uses checksums to ensure that all the data on our servers is intact and is not silently corrupted.