Seagate NAS OS 4 U User Manual page 107

RAID 5 writes data across all hard drives in the volume and a parity block for each data block. If one hard drive
fails, the data can be rebuilt onto a replacement hard drive. No data is lost if a single hard drive fails. However,
if a second hard drive fails before data can be rebuilt on the replacement hard drive, all data in the array is lost.
.A minimum of three hard drives is required to create a RAID 5 volume
RAID 5 offers performance that can approach RAID 0. The strong advantage that RAID 5 gives you is data
protection. Additionally, you still have approximately 75% of the storage capacity of a RAID 0 array (based
:upon total available hard drives and storage capacities). The equation for determining the storage is
( . The size of the hard drive with the smallest capacity in the array)*(Total hard drives-1)
.Example 1: An array is assigned five 3TB hard drives for a total of 15TB. The equation is: 3TB * 4= 12TB
Example 2: An array is assigned three 2TB hard drives and one 3TB hard drive for a total of 9TB. The equation
.is: 2TB * 3= 6TB
RAID 6
RAID 6 writes data across all hard drives in the volume and two parity blocks for each data block. If one hard
drive fails, the data can be rebuilt onto a replacement hard drive. With two parity blocks per data block, RAID 6
.supports up to two hard drive failures with no data loss
RAID 6 synchronizing from a failed hard drive is slower than RAID 5 due to the use of double parity. However, it
is far less critical due to double-disk security. A minimum of four hard drives is required to create a RAID 6
.volume
.RAID 6 offers very good data protection with a slight loss in performance compared to RAID 5
RAID 10
107 10/18/16 Seagate NAS OS 4