When setting up a storage array with 4 drives, the main options to consider are RAID 0, RAID 1, RAID 5, RAID 10, and JBOD.
RAID 0 offers no redundancy but provides maximum storage capacity and performance. Data is striped across all 4 drives, so the total array capacity equals the sum of all drive capacities. Reads and writes are fast since data is spread across multiple disks.
However, RAID 0 provides no protection against drive failure. If one drive fails, all data in the array will be lost. For this reason, RAID 0 is best suited for non-critical data where capacity and speed are most important.
Advantages of RAID 0
- Maximum capacity – Total capacity equals sum of all disks
- Maximum performance – Fastest reads and writes of any RAID level
Disadvantages of RAID 0
- No fault tolerance – Total data loss if any one drive fails
RAID 1 provides redundancy by mirroring data across drives. For a 4 drive array, you would have two sets of mirrored drives. Total capacity equals half the total sum of the drives.
RAID 1 offers excellent read performance since either mirror can satisfy a read request. Writes are slower as data has to be written to both mirrors.
RAID 1 can tolerate the failure of up to half the drives before data loss occurs. For a 4 drive array, you can lose up to 2 drives without losing data. However, once a failed drive is replaced, the RAID will need to rebuild the mirror, which impacts performance.
Advantages of RAID 1
- Excellent read performance
- Can survive failure of up to half the drives
Disadvantages of RAID 1
- 50% storage capacity overhead
- Slower write performance
- Rebuild impacts performance after drive failure
RAID 5 stripes data and parity across all drives. The parity allows the array to recover data in the event of a single drive failure. Total capacity equals sum of all drives minus one drive for parity.
RAID 5 offers good read performance, but writes are slower due to parity calculation. After a drive failure, RAID 5 operates in a degraded state with reduced performance until the failed drive is replaced and data rebuilt.
For a 4 drive RAID 5 array, you can lose any one drive without data loss. However, if a second drive fails before rebuilding occurs, all data will be lost.
Advantages of RAID 5
- Good read performance
- Low storage overhead – Total capacity equals n-1 drives
- Can survive single drive failure
Disadvantages of RAID 5
- Slower write performance due to parity
- Degraded performance in rebuild state
- Total data loss if second drive fails before rebuild
RAID 10 is a nested RAID that combines mirroring and striping for both redundancy and performance. It requires a minimum of 4 drives. Data is striped across two mirrored drive pairs.
RAID 10 provides fast read/write performance by spreading I/O across multiple disks. It can survive failure of up to two drives – one from each mirrored pair. However, rebuilding degrades performance until complete.
Total array capacity equals half the total capacity of all drives. For 4 drives, you get the equivalent capacity of two drives.
Advantages of RAID 10
- Excellent performance
- Can survive two drive failures
Disadvantages of RAID 10
- 50% storage capacity overhead
- Degraded performance during rebuild
JBOD (Just a Bunch of Disks) combines drives into a single logical volume. It provides maximum capacity with no redundancy. Drives appear as one large volume but are not striped for performance.
JBOD is simple to set up and provides maximum storage, but no fault tolerance. If any one drive fails, all data on that drive will be lost. JBOD makes drive failure impact more predictable compared to RAID 0.
Advantages of JBOD
- Simple configuration
- Maximum storage capacity
Disadvantages of JBOD
- No performance improvement over single disk
- No fault tolerance
The best array for 4 drives depends on your requirements for capacity, performance, and fault tolerance:
- RAID 0 – Maximum performance and capacity but no redundancy. Best for non-critical data.
- RAID 10 – Balances performance and redundancy. Can survive two drive failures. Good for critical data and applications.
- RAID 5 – Good performance, capacity, and redundancy for a low cost. Can survive one drive failure.
- RAID 1 – Excellent read performance and redundancy but lower capacity. Good for read-intensive workloads.
- JBOD – Maximum capacity but no performance improvement or fault tolerance. Useful for archival data.
The best solution depends on your specific needs. RAID 10 provides a good balance for most scenarios but has a 50% capacity overhead. RAID 5 is efficient if you only need to survive one drive failure. For non-critical data, RAID 0 provides maximum performance and capacity.
Here is a table summarizing the characteristics of each RAID level:
|RAID Level||Redundancy||Capacity||Read Performance||Write Performance|
|RAID 5||Good||n-1 drives||Excellent||Good|
Understanding Fault Tolerance
Fault tolerance is a key factor when choosing a RAID level. Here is an overview of how each option provides fault tolerance:
- RAID 0 – No fault tolerance. Any drive failure destroys the array.
- RAID 1 – Excellent tolerance for up to 50% drive failures. For 4 drives, it can survive if 2 fail.
- RAID 5 – Good tolerance for one drive failure. The array can rebuild after a single failed drive.
- RAID 10 – Excellent tolerance up to two drive failures in separate mirrors. For 4 drives, it can survive if 1 from each mirror fails.
- JBOD – No fault tolerance. The failure of any drive results in data loss on that drive.
When choosing a RAID level, consider how many drive failures your application can sustain. Higher redundancy comes at the cost of lower usable capacity. The best balance depends on your needs for capacity, performance, and redundancy.
Recovering from Drive Failures
Most RAID levels provide redundancy to survive drive failures. However, performance will be impacted until the failed drive is replaced and data rebuilt.
After replacing a failed drive, the array controller will rebuild the data automatically. The rebuild time depends on the RAID level and drive capacity. Rebuilding large drive arrays can take many hours during which performance will be degraded.
To minimize downtime, select enterprise-grade drives designed for RAID environments. Monitor drive health proactively to replace failures early. Consider hot spare drives which can immediately start a rebuild if a drive fails.
Combining RAID Levels
In some cases, you may want to combine multiple RAID levels to meet capacity, performance and redundancy needs:
- RAID 10 – Combination of RAID 1 mirroring and RAID 0 striping. Provides performance, redundancy, but lower capacity.
- RAID 50 – Combination of RAID 5 and RAID 0. Improves RAID 5 performance but increases risk of data loss.
- RAID 60 – Combination of RAID 6 and RAID 0. Adds double distributed parity for high fault tolerance and performance.
Nested RAID levels allow you to blend the characteristics of different RAID types. For example, RAID 50 provides the redundancy of RAID 5 with the performance of RAID 0. Experiment to find the right balance for your specific needs.
Hardware vs. Software RAID
RAID can be implemented in hardware or software:
- Hardware RAID – Uses a dedicated RAID controller to manage the array. Offloads processing from main CPU.
- Software RAID – Managed by OS and drivers. No hardware cost but uses CPU resources.
Hardware RAID provides better performance as it has dedicated processors and memory. Software RAID uses system resources, so can impact performance for other applications.
However, hardware RAID relies on proprietary controllers. If the controller fails, data recovery is difficult. With software RAID, drives can be moved to another system easily.
For enterprise and mission critical systems, hardware RAID is preferred. For home builds or labs, software RAID provides a low cost alternative.
Storage needs grow over time. Some RAID levels make expanding arrays easier than others:
- RAID 0 – Additional drives can be added to increase total capacity and performance.
- RAID 1 – Drives must be added in pairs. Existing data is mirrored to new drives.
- RAID 5 – Drives can be added one at a time. Total capacity increases but not redundancy.
- RAID 10 – Drives must be added in pairs. Capacity increases but existing data remains mirrored on original set.
- JBOD – New drives are simply added to end of array. Very easy to expand but no performance gain.
For maximum upgradability, RAID 0, RAID 5, or JBOD are best. For RAID 1 and 10, drives must be added in pairs. Upgrades require rebuilding existing data to new disks.
Caching and Controllers
RAID performance is heavily influenced by caching and controller capabilities:
- Large cache improves read/write performance by buffering data flow.
- Faster processors speed up parity calculations and data transfers.
- More I/O lanes increase parallelism between drives.
- Newer controllers support faster drive interfaces like NVMe and PCIe.
When configuring hardware RAID, choose controllers with large caches, fast processors, and many I/O lanes. Use the fastest drive interfaces supported. This minimizes bottlenecks and maximizes throughput.
Many motherboards include basic RAID support. For performance-critical applications, invest in a dedicated hardware RAID controller with high-end specs.
Monitoring and Alerting
Actively monitoring RAID health can prevent issues:
- Monitor drive health statistics like utilization, errors, temperature.
- Trigger alerts for signs of impending failure.
- Track rebuild progress and completion.
- Log all configuration changes and administrative actions.
Many RAID controllers include management software to monitor arrays and trigger alerts. For software RAID, OS tools like mdadm provide monitoring capabilities.
Be proactive and take immediate action on any warnings. Catching issues early maximizes uptime and avoids data loss.
Even redundant RAID arrays can still fail and result in data loss. Regular backups are essential:
- Back up critical data on a routine schedule – daily or weekly.
- Store backups offline or off-site to protect from catastrophic failure.
- Test backups regularly to verify completeness and integrity.
- Document backup and restore procedures.
Ideally combine RAID with networked storage and remote backups for maximum data protection and availability.
If using software RAID via the operating system, the main solutions are:
- Windows – Windows Storage Spaces support software RAID 0, 1, 5, 6 and 10.
- Linux – mdadm provides software RAID support in Linux, including nested levels.
- Hardware Agnostic – Solutions like ZFS and Ceph support proprietary RAID configurations and are OS agnostic.
Software RAID is a good choice for cost-effective redundant arrays. Make sure to factor in CPU overhead when evaluating performance.
The best RAID configuration for 4 drives depends on your priorities for performance, capacity, and redundancy. Common choices include:
- RAID 10 for optimal performance and redundancy.
- RAID 5 for a good balance of capacity and redundancy.
- RAID 0 when capacity and speed are most important.
- RAID 1 for excellent redundancy and read performance.
Monitor array health closely, rebuild failed drives promptly, and maintain good backups for maximum uptime. Invest in a quality RAID controller to maximize performance capabilities.