Choose a RAID Type

RAID (Redundant Array of Independent Disks) is a data storage technology that allows multiple drives to be combined into a single storage space. There are different types of RAID, each providing different levels of performance, storage capacity, and reliability.

This article provides a brief overview of RAID types supported by Synology Unified Controller, including implementation requirements as well as advantages and disadvantages.

Support RAID Types

This table provides a brief overview of different RAID types supported by Synology Unified Controller, including storage capacity, the minimum number of drives required for the RAID type, and the number of drive failures that can be tolerated before data loss occurs.

RAID Type	Number of Drives	Tolerable Drive Failures	Description	Storage Capacity
Basic	1	0	Composed of one drive as an independent unit. Does not provide data redundancy.	1 x (Drive size)
JBOD	≧1	0	Combines a collection of drives into a single storage space, with a capacity equal to the sum of all drives' capacity. Does not provide data redundancy.	Sum of all Drive sizes
RAID 0	≧2	0	Features "striping," a process of dividing data into blocks and spreading the data blocks across several drives to enhance performance. Does not provide data redundancy.	Sum of all drive sizes
RAID 1	2	1	Writes identical data to all the drives simultaneously. Provides data redundancy.	Smallest drive size
	3	2
	4	3
RAID 5	≧3	1	Implements block-level striping with parity data distributed across all member drives, thus providing data redundancy more efficiently than RAID 1.	(N – 1) x (Smallest drive size)
RAID 6	≧4	2	Implements two layers of data parity to store redundant data equal to the size of two drives, providing a greater degree of data redundancy than RAID 5.	(N – 2) x (Smallest drive size)
RAID 10	≧4 (even number)	Half of the total drives	Provides the performance of RAID 0 and data protection level of RAID 1, combining drives into groups of two in which data is mirrored.	(N / 2) x (Smallest drive size)
RAID F1	≧3	1	Implements block-level striping with parity data distributed across all member drives. A certain drive will have more parity information. Recommended for an all-flash array.	(N – 1) x (Smallest SSD size)

Note:

RAID types except for "Basic" are only available on certain models depending on the number of drive slots and number of installed drives.
RAID F1 is available on specific models only. For more information, please visit Synology website.
"N" represents the total number of drives within the volume.

RAID 0

RAID 0 combines two or more drives to increase performance and capacity but provides no fault tolerance. A single drive failure will result in the loss of all data on the array. RAID 0 is useful for non-critical systems where a high price/performance balance is required.

RAID 1

RAID 1 is most often implemented with two drives. Data on the drives are mirrored, providing fault tolerance in case of drive failure. Read performance is increased while write performance will be similar to a single drive. A single drive failure can be sustained without data loss. RAID 1 is often used when fault tolerance is key, while space and performance are not critical requirements.

RAID 5

RAID 5 provides fault tolerance and increased read performance. A minimum of three drives is required. RAID 5 can sustain the loss of a single drive. In the event of a drive failure, data from the failed drive is reconstructed from parity striped across the remaining drives. As a result, both read and write performance is severely impacted while a RAID 5 array is in a degraded state. RAID 5 is ideal when space and cost are more important than performance.

RAID 6

RAID 6 is similar to RAID 5, except it provides another layer of striping and can sustain two drive failures. A minimum of four drives is required. The performance of RAID 6 is lower than that of RAID 5 due to this additional fault tolerance. RAID 6 becomes attractive when space and cost are important and sustaining multiple drive failures is required.

RAID 10

RAID 10 combines the benefits of RAID 1 and RAID 0. Read and write performance is increased, but only half of the total space is available for data storage. Four or more drives are required making the cost relatively high, but the performance is great while providing fault tolerance at the same time. In fact, a RAID 10 can sustain multiple drive failures -- provided the failures are not within the same sub-group. RAID 10 is ideal for applications with a high input/output demand such as database servers.

RAID F1

RAID F1 applies the mechanism of RAID 5, providing fault tolerance and increased read performance. With RAID F1, however, a certain drive will have more parity information to accelerate its aging, thus preventing all the drives from coming to their end of lifespan at the same time. This may subtly affect its performance when compared to RAID 5. A minimum of three drives is required. RAID F1 can sustain the loss of a single drive. In the event of a drive failure, data from the failed drive is reconstructed from parity striped across the remaining drives. As a result, both read and write performance is severely impacted while a RAID F1 array is in a degraded state. RAID F1 is ideal for an all-flash array.

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