A RAID group helps avoid RAID failure when drives are added to a single RAID array for storage expansion. With this feature, you can configure multiple RAID arrays in a storage pool to balance your device’s storage capacity and data security.

RAID group

In a normal storage pool, no matter how many drives there are in a RAID array, the fault tolerance is fixed according to the RAID type. Adding more drives to a single RAID array for storage expansion may increase the chance of RAID failure.

A RAID group uses drives to create multiple RAID arrays, and then combines them together as a storage pool via Logical Volume Manager (LVM). By doing this, fault tolerance increases according to the number of RAID arrays in the storage pool. The capacity may be reduced, but the fault tolerance will increase to enhance reliability.

Example 1:

A storage pool with 24 drives is created with RAID 5 (with 1-drive fault tolerance). Although the total capacity is the capacity of drive multiplied by 23, RAID failure only occurs if 2 drives fail.

Example 2:

A RAID group with 24 drives is created with RAID 5, and the maximum drive number per RAID is 6. Each RAID array has a fault tolerance of 1 drive, so the RAID group has a maximum of 4-drive fault tolerance in total. The total capacity is the capacity of available drives per array multiplied by the number of RAID arrays. In this case, the total capacity can be calculated as follows:

The capacity is less than having a storage pool with 24 drives, but the fault tolerance is higher. RAID failure only occurs if 2 drives fail within the same array.

Limitations

• Refer to this article for applicable models.
• Supported RAID types: RAID 5, RAID 6, RAID F1.
• Maximum number of drives per RAID:

DSM 7.0 and above

DSM 6.2 and below