A redundant array of independent disks (RAID) protects network-attached storage (NAS) and other devices from data loss when multiple drives are used. On a NAS, multiple drives can be combined into a single volume or storage pool, making it easier to work with data on multiple devices. A RAID achieves the same result but offers the benefit of redundancy through reserved backup data and drive fault tolerance. Combining a NAS with RAID is an easy way to create a powerful yet easy-to-use storage solution for the local area network (LAN).
What is RAID?
RAID is a feature supported by most (if not all) NAS operating systems that allows you to clone data across multiple drives. RAID is divided into three aspects and can help you protect against data loss through data striping, mirroring, and parity. Data striping involves splitting blocks into smaller blocks and storing them on separate disks, mirroring involves cloning data from one drive to another, and parity involves adding error correction codes to stored data. While RAID should not be considered a data backup, it does help prevent data loss due to the inevitable failure of one or more of your drives.
Why use RAID with NAS?
A NAS typically has multiple drives installed in the chassis. These can be combined into a single storage pool that can store data from multiple clients. However, to prevent potential drive failures, we need a RAID. No drive lasts forever, not even an SSD. Mechanical drives have many moving parts, all of which are potential points of failure. Should a drive in your RAID fail, the operating system can recover it by using recovery data and rebuilding the RAID using a spare drive. Depending on the RAID you use, you will have a failure tolerance of at least one drive.
The process for creating a RAID on your NAS is similar regardless of manufacturer and operating system. When you set up a new NAS, you configure the drives through the installer. When you add new drives after installing the operating system, this is usually done through the drive management app. Once it's running, you'll barely notice it's there. Depending on the RAID you choose, you may lose storage space as part of the storage pool is used to store recovery data. This could be one or two whole drives, so plan accordingly to make sure you have enough space.
Different RAID types
RAID 1 is the simplest form of RAID. Also known as mirroring, data is duplicated across all drives. An entire drive is reserved for parity, reducing the total capacity of the pool by half. This provides the fastest recovery should one drive fail. RAID 1 is better suited for smaller NAS deployments with two drives. For more than three drives, I would suggest moving up to RAID 5 or 6. With a drive failure tolerance of one and two respectively, they are ideal for those who need to store a lot of data on NAS. Parity data is stored on one drive, which is then used to rebuild the RAID should one fail. RAID 1+0 is essentially RAID 0 and RAID 1.
Regardless of which RAID you choose (other than RAID 0 or JBOD), you sacrifice some storage capacity for drive redundancy. RAID can also impact performance because the drive handles parity, so write speeds are slightly reduced.
Using RAID does not back up your data
I stress this point over and over again, but it's important to understand that using RAID does not mean you're backing up data. Yes, your RAID may be able to automatically recover from a drive failure without losing a single byte of data, but there's always the risk that something could happen to the RAID that could cause files to become corrupted or lost. Data can be corrupted by firmware errors or system glitches. The RAID cannot recover the data without relying on a backup as a reference. There's even the possibility that the RAID controller could fail.