RAID 5 is perhaps the most common secure RAID level, and requires at least three drives. It combines striping with parity to ensure your data is extra secure.

Like all RAID setups, RAID 5 combines multiple hard drives into a single unit. Consisting of block-level striping with distributed parity, RAID 5 requires that all but one drive be present in order to operate. Upon the failure of a drive, reads can be calculated from the distributed parity, ensuring no data is lost.

RAID 5 requires at least 3 hard drives to operate, although it can work with up to 16. RAID 5 uses the striping techniques used in RAID 0, where data is striped across the disks in the array. RAID 0 requires a minimum of two disks, and data is striped across the disks, producing essentially a hard drive with double the storage capacity and increased speeds, since data can be accessed from both disks at the same time. However, if one drive in a RAID 0 array fails, then the data will be inaccessible from the second drive. This is the main drawback of RAID 0 – it’s lack of fault tolerance – and why RAID 5 is the more preferable option if you’re looking to protect your data.

In a RAID 5 array, you have increased storage capacity as with RAID 0, although you lose one drive where the parity information is stored. For example, if you have a RAID 5 array with three 2TB hard drives, the total usable storage will be 4TB, as one of the 2TB drives will be used to store the parity data. RAID 5 arrays have slower write speeds, as parity information must be written alongside the actual data. On the other hand, read speeds are very fast. If a drive in a RAID 5 array fails, all the data is still accessible, while the failed drive is being replaced and the RAID controller rebuilds data onto the new drive.

There are two main drawbacks of RAID 5. Firstly, if one of the disks in the array fails and it has a particularly large storage capacity, for example 4TB, the rebuild time may be considerable, depending on the number of factors including the speed of the RAID controller. Rebuild time could potentially take up to a day or even longer. Secondly, if another disk in the array fails during the rebuild time, then you’re in trouble, as the data will not be accessible. This is why RAID is not a substitute for a backup.