RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drives to achieve greater levels of performance, redundancy, or both. The main goals of RAID are to protect against data loss in case of drive failure and improve performance for demanding applications.
With RAID, data is distributed across multiple drives in a redundant fashion. If one drive fails, the data can still be recovered from the remaining drives. There are several RAID “levels” that offer different combinations of performance and fault tolerance. For example, RAID 0 stripes data across drives for speed, while RAID 1 duplicates data across drives for redundancy.
When choosing a RAID level for a given scenario, factors such as performance needs, number of drives, and tolerance for drive failure must be weighed. This article explores the most common RAID levels and provides recommendations for configuring RAID with 4 disks.
RAID 0
RAID 0, also known as disk striping, is a RAID configuration that stripes data across multiple disks for increased performance (Source). It does not provide any redundancy, meaning if one disk fails, all data will be lost. RAID 0 spreads data evenly across two or more disks without parity information (parity bits are used for reconstruction of lost data in some other RAID levels). This allows for high I/O performance but provides no fault tolerance (Source).
RAID 0 is best suited for non-critical data where performance is more important than redundancy. Some common uses are for scratch disks, video editing, and gaming. The main benefit of RAID 0 is increased read and write speeds due to spreading data across multiple disks. However, it comes at the cost of increased risk because a single disk failure results in total data loss.
RAID 1
RAID 1, also known as “mirroring”, is a data storage configuration that writes identical copies of data to two or more disks (cite: https://medium.com/@PITSGlobalDataRecoveryServices/raid-1-explained-the-power-of-duplicate-data-53e9dbeb92b1). This redundancy allows continued operation if one disk fails. RAID 1 requires at least two hard disks to duplicate the data, but some configurations can use more disks. When data is written to the RAID 1 array, both disks are simultaneously updated with the same information. This provides data redundancy and fault tolerance in the event a drive fails or data becomes corrupted. If one drive fails, the system can instantly switch to the other drive without any loss of data or service interruption. The failed drive can then be hot-swapped for a new one and the new disk will be rebuilt and synchronized from the surviving drive (cite: https://pcsite.co.uk/what-is-raid-1/).
RAID 1 is considered one of the most robust and reliable RAID levels. It provides excellent performance for read operations, since the data can be accessed from either disk simultaneously. However, RAID 1 is inefficient for storage capacity since the available disk space is equal to the capacity of one disk. It also has slower write performance compared to RAID 0 since the data has to be written twice. Still, RAID 1 is an excellent choice when data redundancy and fault tolerance are critical requirements.
RAID 5
RAID 5 spreads data across all the drives and uses parity information stored on one drive to reconstruct data if a drive fails. It stripes data across multiple disks like RAID 0, but also reserves space on one disk for parity information. The parity information allows for data recovery in the event a single drive fails.
RAID 5 requires at least 3 disks to operate. It stripes data across the disks in chunks. For each set of chunks, one disk is used to store parity information that can be used to reconstruct data if needed. For example, with 4 disks the first chunks of data would be striped across disks 1-3 while disk 4 stores the parity. The next chunks would stripe across disks 2-4 with disk 1 storing parity, and so on.
The main benefits of RAID 5 are increased read performance thanks to striping, and single disk fault tolerance thanks to the parity drive. The tradeoff is reduced write performance and storage capacity compared to a single disk, since parity information needs to be calculated and written alongside the data. Overall, RAID 5 provides a good balance of performance, capacity and fault tolerance for small server or NAS environments.
RAID 10
RAID 10, also known as RAID 1+0, is a combination of RAID 0 and RAID 1. It provides mirrored stripes, which means the data is both striped across multiple disks like RAID 0 and duplicated like RAID 1. This configuration provides the performance benefits of RAID 0 and the fault tolerance of RAID 1.
With RAID 10, the data is striped across two or more disks and each stripe is mirrored onto another set of disks. For example, with four disks you would have two stripes mirrored onto two sets of disks. This provides high read and write speeds since data can be accessed in parallel across multiple disks. At the same time, if one disk fails, the mirrored data is still available from the other set of disks.
Some key advantages of RAID 10 include:
- High performance – reads and writes can be distributed across multiple disks
- Fault tolerance – can withstand multiple drive failures so long as no more than one drive fails in each mirrored set
- Ideal for applications requiring high performance and availability
The tradeoff is that RAID 10 requires at least four disks and equivalent capacity is lost to redundancy. Still, with its combination of speed and redundancy, RAID 10 is a popular choice for mission critical systems.
RAID 6
RAID 6 is a popular option for arrays with 4 or more disks. It utilizes double distributed parity, meaning there are two parity disks rather than just one (like in RAID 5). This provides protection against up to two disk failures, making RAID 6 a good choice for larger arrays where the probability of multiple disk failures is higher. RAID 6 can sustain up to two failed disks without losing data 1.
With double distributed parity, the parity information is spread evenly across all the disks. If one disk fails, the array can instantly re-create the missing data from the parity information on the other disks. And if a second disk fails, the second set of parity information can be used to recover that data. This provides excellent redundancy and fault tolerance 2.
The tradeoff with RAID 6 is slower write performance compared to RAID 5, as more complex parity calculations have to be performed with each write. However, RAID 6 offers far superior protection compared to RAID 5 in larger arrays where multiple disk failures are a real possibility.
RAID 50
RAID 50 combines the distributed parity of RAID 5 with the striping of RAID 0 for better performance and capacity when using many disks. It stripes RAID 5 arrays together, so you need a minimum of 6 disks for a RAID 50 setup (Source 1).
RAID 50 provides good read performance since data is striped across multiple disks. Write performance is slower than RAID 10 due to the parity calculations required by RAID 5. RAID 50 can tolerate multiple disk failures, as long as no more than 1 disk fails per RAID 5 array. If using 6 disks, it can handle 2 disk failures (Source 2).
The main advantage of RAID 50 over RAID 5 is the greater number of disks supported. RAID 50 scales better for large disk arrays by striping RAID 5 sets. This makes RAID 50 a good choice for applications requiring high capacity, redundancy, and moderate performance with many disks (Source 3).
RAID 60
RAID 60 is an advanced form of RAID that combines both striping and mirroring for increased performance and reliability. It requires a minimum of 8 disks 1. RAID 60 essentially stripes RAID 6 arrays instead of RAID 5 arrays like in RAID 50. This provides additional fault tolerance compared to RAID 50, as each RAID 6 sub-array can withstand the loss of 2 disks before complete failure 2.
The tradeoff is potentially lower performance compared to RAID 50 due to the heavier parity calculations required by the RAID 6 sub-arrays. However, RAID 60 is an ideal choice when data reliability and integrity are critical, and when the budget allows for at least 8 disks. It protects against dual disk failures in each sub-array and provides good performance from striping, making it well-suited for mission-critical storage systems.
Recommendations
When choosing a RAID configuration for a home NAS with 4 disks, the best option depends on your specific needs and priorities.
For maximum performance, RAID 0 stripes data across all 4 disks. This allows for very fast read/write speeds but offers no redundancy. RAID 0 is best for non-critical data where speed is the top concern.
For the best balance of performance and redundancy, RAID 10 mirrors 2 disks into a RAID 1 array, then stripes them. This provides excellent speeds while protecting against 2 disk failures. RAID 10 is a great choice for media storage and productivity.
For the maximum protection, RAID 6 can sustain up to 2 disk failures by using 2 parity disks. This provides excellent redundancy for critical data at the cost of slower write speeds.
For a balance of redundancy and storage, RAID 5 stripes data and parity across all disks, allowing for 1 disk failure. RAID 5 offers good protection for increased storage, but rebuild times can be slow.
Conclusion
In summary, the key points from this piece are:
- RAID 0 offers the best performance but has no redundancy.
- RAID 1 is easy to setup and provides good redundancy but uses 50% of disks for parity.
- RAID 5 provides a balance of performance and redundancy but write speeds are slow.
- RAID 6 offers excellent redundancy but write speeds suffer.
- RAID 10 combines RAID 0 and 1 for performance and redundancy but uses 50% of disks for parity.
Based on the pros and cons of each RAID level, I would recommend either RAID 10 or RAID 6 for a 4 disk array, depending on your priorities. RAID 10 is best for performance while RAID 6 provides the best redundancy. Just be aware RAID 10 uses 50% of disks for parity while RAID 6 uses 2 disks.
