Redundant Array of Independent Disks, or RAID, is a way of saving content on multiple hard disk drives at the same time. A RAID might be software or hardware depending on the drives that are used - physical or logical ones, still what is common between them is that they all perform as just a single unit where data is saved. The top advantage of using a RAID is redundancy since the info on all drives shall be identical all the time, so even in the event that some drive fails for whatever reason, the data will still be available on the rest of the drives. The general performance is also enhanced because the reading and writing processes could be split between multiple drives, so a single one will not be overloaded. There are different sorts of RAIDs where the functionality and fault tolerance can vary according to the specific setup - whether info is written on all drives in real time or it is written on a single drive and afterwards mirrored on another, what number of drives are used for the RAID, and so on.
RAID in Shared Hosting
The drives that we use for storage with our state-of-the-art cloud Internet hosting platform are not the standard HDDs, but super fast solid-state drives (SSD). They operate in RAID-Z - a special setup designed for the ZFS file system that we use. Any content that you upload to the shared hosting account will be kept on multiple hard disks and at least one of them will be used as a parity disk. This is a special drive where a further bit is added to any content copied on it. In case a disk in the RAID stops functioning, it'll be replaced without service interruptions and the information will be recovered on the new drive by recalculating its bits using the data on the parity disk along with that on the remaining disks. This is done in order to guarantee the integrity of the data and together with the real-time checksum validation that the ZFS file system runs on all drives, you will never need to worry about losing any data no matter what.