Redundant Array of Independent Disks, or RAID, is a method of saving content on multiple hard disks at the same time. A RAID might be software or hardware depending on the hard drives that are used - physical or logical ones, but what is common between them is that they all work as a single unit where data is saved. The biggest advantage of employing a RAID is redundancy since the info on all the drives shall be the same all the time, so even if one of the drives fails for some reason, the information will still be available on the remaining drives. The overall performance is also enhanced because 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 functionality and fault tolerance may vary depending on the particular setup - whether your data is written on all the drives real-time or it is written on a single drive and afterwards mirrored on another, what amount of drives are used for the RAID, and many others.
RAID in Hosting
The hard drives that we employ for storage with our innovative cloud web hosting platform are not the standard HDDs, but extremely fast solid-state drives (SSD). They function in RAID-Z - a special setup developed for the ZFS file system that we work with. All the content that you upload to your hosting account will be saved on multiple hard drives and at least one will be used as a parity disk. This is a special drive where a further bit is added to any content copied on it. If a disk in the RAID stops working, it'll be changed without any 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 to guarantee the integrity of the information and along with the real-time checksum verification that the ZFS file system runs on all drives, you will never have to be concerned about losing any data no matter what.