RAID (Redundant Array of Independent Disks) is a data storage technology that allows multiple hard 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 DiskStation, including implementation requirements as well as advantages and disadvantages.
This table provides a brief overview of different RAID types supported by DiskStation, including storage capacity, the minimum number of hard drives required for the RAID type, and the number of hard drive failures that can be tolerated before data loss occurs.
| Volume Type | Number of HDD | Tolerable Hard Drive Failures | Description | Volume Capacity |
|---|---|---|---|---|
| SHR | 1 | 0 |
|
1 x (HDD size) |
| 2-3 | 1 | Optimized by the system. | ||
| ≧4 | 1-2 | |||
| Basic | 1 | 0 |
|
1 x (HDD size) |
| JBOD | ≧2 | 0 |
|
Sum of all HDD sizes |
| RAID 0 | ≧2 | 0 |
|
Sum of all HDD sizes |
| RAID 1 | 2 | 1 |
|
Smallest HDD size |
| 3 | 2 | |||
| 4 | 3 | |||
| RAID 5 | ≧3 | 1 |
|
(N – 1) x (Smallest HDD size) |
| RAID 6 | ≧4 | 2 |
|
(N – 2) x (Smallest HDD size) |
| RAID 10 | ≧4 (even number) |
Half of the total HDD |
|
(N / 2) x (Smallest HDD size) |
Synology Hybrid RAID (SHR) is an automated RAID management system, designed to simplify storage management and meet the needs of new users who are unfamiliar with RAID types.
SHR can combine different sized hard drives to create a storage volume with optimized capacity and performance, wasting less hard drive space and providing a more flexible storage solution. When sufficient hard drives are included, SHR allows for 1- or 2-disk redundancy - meaning the SHR Volume can suffer up to one or two failed hard drives without experiencing data loss.
RAID 0 combines two or more hard drives to increase performance and capacity, but provides no fault tolerance. A single hard 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 is most often implemented with two hard drives. Data on the hard drives are mirrored, providing fault tolerance in case of hard drive failure. Read performance is increased while write performance will be similar to a single hard drive. A single hard 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 provides fault tolerance and increased read performance. A minimum of three hard drives is required. RAID 5 can sustain the loss of a single hard drive. In the event of a hard drive failure, data from the failed hard drive is reconstructed from parity striped across the remaining hard 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 is similar to RAID 5, except it provides another layer of striping and can sustain two drive failures. A minimum of four hard 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 hard drive failures is required.
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 hard 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 hard 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.