RAID 5E is a type of nested RAID (redundant array of independent disks) level. With an integrated hot spare drive, it is an extension of RAID 5.
The letter “E” stands for “enhanced” or “extended” in RAID 5E array. In a traditional RAID 5 architecture with a hot spare drive - which is actively utilized in the array operations – the hot spare drive sits next to the array waiting for a drive to fail, at which point the hot spare drive is made available and the array rebuilds the data set with the new hardware.
Here are some advantages to this operational method:
• You’re aware of the fact that the drive that would have been used as a hot spare is in functional condition.
• Since there is an additional drive included, further distributing the array’s I/O load.
The capacity of a RAID 5E array is exactly the same as the capacity of a RAID 5 array which contains a hot spare drive. In such a condition, there’s a chance you lose two disks’ capacity – one disk’s worth for parity and another for the hot spare. That’s why RAID 5E needs that you use at least four drives, and up to eight or sixteen drives can be supported in a single array, depending on the controller.