When setting up a storage system, one of the most important decisions is choosing the right RAID level. RAID, which stands for Redundant Array of Independent Disks, allows you to spread and replicate data across multiple drives to enhance performance, capacity, and fault tolerance. With so many RAID levels available, how do you determine what RAID is best for your data storage needs? The quick answer depends on your priorities – performance, capacity, availability, or budget. We’ll explore the pros and cons of different RAID levels so you can make an informed decision.
What is RAID?
RAID is a technology that combines multiple physical disk drives into a single logical unit. Data is distributed across the drives according to the specific RAID level’s design. The main reasons to implement RAID are to achieve redundancy, improve performance, and increase storage capacity beyond what a single drive can provide.
Some key advantages of using RAID include:
- Redundancy – RAID allows data to be mirrored or striped across drives. If one drive fails, data can be rebuilt from the remaining drives.
- Performance – By spreading data across multiple disks, I/O operations can be performed in parallel to improve speed.
- Capacity – Multiple drives add up to a larger total storage pool.
There are various RAID levels, each optimizing for different factors – performance, capacity, or redundancy. We’ll examine the most common RAID levels and their use cases next.
Common RAID Levels
RAID 0
RAID 0, also known as disk striping, splits data evenly across two or more drives. The benefit of RAID 0 is that disk performance is greatly improved by spreading the I/O load across multiple drives. However, RAID 0 provides no data redundancy – if one drive fails, all data is lost.
Use cases:
- Improving disk performance for temporary storage
- Gaining capacity by combining drives
Pros:
- Fast performance
- Full capacity of all drives usable
Cons:
- No redundancy
- Total failure if any drive dies
RAID 1
RAID 1, or disk mirroring, creates an exact copy of data on two or more drives. If one drive fails, data remains fully intact and accessible on the mirror drive(s). RAID 1 provides data redundancy and fault tolerance but cuts the total storage capacity in half.
Use cases:
- Critical data that requires high availability
- Small-scale servers that need redundancy
Pros:
- Easy to implement and manage
- Data protection from single drive failure
Cons:
- 50% storage efficiency
- Slow write performance
RAID 5
RAID 5 stripes data and parity information across a minimum of three drives. If a single drive fails, data can be rebuilt using the parity drive. Compared to RAID 1, RAID 5 provides redundancy with less capacity loss – only one drive worth of space is needed for parity. However, write speeds are slower due to parity calculation.
Use cases:
- File and application servers
- Network Attached Storage (NAS)
- Disk-intensive applications like databases
Pros:
- Good redundancy with minimal capacity loss
- Decent performance for reads and writes
Cons:
- RAID rebuild time is slow after drive failure
- Performance degradation during rebuilds or recovery
RAID 6
RAID 6 provides double distributed parity, allowing for data recovery with up to two disk failures. It requires a minimum of four drives with two drives worth of capacity used for parity. RAID 6 offers high fault tolerance but slower write speeds.
Use cases:
- Mission critical systems that need high availability
- Large disk arrays where drive failures are more likely
Pros:
- Can sustain two drive failures
- Protection against data loss
Cons:
- High disk overhead for parity (2 drives)
- Slower write performance than RAID 5
RAID 10
RAID 10 combines both mirroring and striping, providing redundancy and performance. Data is striped across drives and also mirrored, requiring an even number of disks. Rebuild times are faster compared to RAID 5/6 as only the mirror drive needs to be rebuilt in case of failure.
Use cases:
- Database servers and other transactional applications
- High performance storage with redundancy
Pros:
- Fast performance for reads and writes
- Full redundancy and fault tolerance
Cons:
- 50% storage efficiency
- Higher hardware cost
RAID Comparison Table
| RAID Level | Minimum Drives | Data Redundancy | Fault Tolerance | Storage Efficiency | Read Performance | Write Performance |
|---|---|---|---|---|---|---|
| RAID 0 | 2 | No | No | 100% | Excellent | Excellent |
| RAID 1 | 2 | Yes | 1 Drive | 50% | OK | Average |
| RAID 5 | 3 | Yes | 1 Drive | 67% – 94% | Good | OK |
| RAID 6 | 4 | Yes | 2 Drives | 50% – 88% | Good | Poor |
| RAID 10 | 4 | Yes | 1 Drive per mirror | 50% | Excellent | Excellent |
Factors to Consider
When selecting a RAID level, there are several factors to take into account:
Availability and Redundancy
If uptime and data availability are critical, choose a redundant RAID level like RAID 1, 5, 6, or 10. RAID 0 offers no redundancy. RAID 6 offers the highest level of fault tolerance, allowing for up to two drive failures.
Performance
RAID 0 and RAID 10 provide the best overall performance for demanding applications like databases or web servers. RAID 5/6 have slower write speeds due to parity calculation.
Drive Costs
Higher RAID levels require more drives, which adds to the total storage cost. RAID 0 is most cost efficient as it maximizes drive capacity. RAID 1 and RAID 10 have a 50% storage efficiency rate.
Rebuilding and Recovery
In case of a drive failure, rebuild and recovery times can impact workload performance. RAID 1 and RAID 10 can be quickly rebuilt from the surviving mirror. RAID 5/6 rebuilds take much longer.
Scalability
RAID levels like RAID 5, 6, and 10 can be easily scaled by adding more drives. Mirroring in RAID 1 is limited to the capacity of two drives. Scaling also improves performance by spreading I/O across more drives.
Manageability
The administrative overhead depends on the RAID level – RAID 0 is simple to manage while configuring and maintaining parity in RAID 5/6 has more complexity. Look for hardware RAID solutions that simplify management.
RAID Use Cases
Transactional Database Servers
Database servers require high availability, fast I/O performance, and data protection. RAID 10 provides mirroring for redundancy along with striping to spread reads/writes across multiple disks for speed.
Business-Critical File Servers
For critical data, fault tolerance is key. A RAID 6 array can sustain up to two drive failures yet still recover data. Slower performance is an acceptable trade-off for high availability.
Media Editing and Design
Performance is the top priority for audio, video, or graphics editing. Use RAID 0 to maximize speed and capacity without redundancy. Have a good backup plan as RAID 0 offers no protection against drive failure.
Personal Desktop Storage
On a budget, consider RAID 1 which duplicates data on two disks. A pair of 2TB drives yields 2TB of redundant storage for safeguarding personal files and media – all protected against a single disk failure.
Network Attached Storage (NAS)
Small business NAS devices often use RAID 1 or RAID 5. RAID 1 allows for easy setup using just two large drives with mirroring for redundancy. RAID 5 handles more drives while providing efficient use of capacity.
Virtualized Servers
Hypervisors and virtual machine storage have mixed workloads with applications needing high performance while virtual machine files demand larger capacity. A combination of RAID 1 for host hypervisor storage and RAID 5/6 for guest VMs can help balance needs.
Software vs. Hardware RAID
RAID can be implemented in software or hardware:
Software RAID
- Managed at the operating system level
- More flexibility in RAID management
- Lower cost, uses existing server storage drives
- Some CPU overhead for RAID processing
Hardware RAID
- Dedicated RAID controller required
- Vendor specific management tools
- Improved performance – offloads RAID from main CPU
- Additional cost for RAID cards
Software RAID is a good option for smaller servers and allows using the server’s existing disks. Hardware RAID comes with better performance and more enterprise capabilities, at an added cost. For mission critical systems, the investment in hardware RAID controllers provides benefits like caching, battery backups, and connection interfaces.
The RAID Controller
Hardware RAID solutions require a RAID controller – an expansion card installed in a server that enables hardware RAID capabilities. Key factors when choosing a RAID controller include:
- RAID Levels Supported – Entry level cards may only support RAID 0/1 while enterprise controllers offer RAID 5/6.
- Drive Connections – Support for SATA, SAS, NVMe will determine type of drives usable.
- Cache Memory – More cache improves read/write performance.
- Backend Connectivity – Interface like PCIe 3.0 provide faster CPU to controller bandwidth.
- Reliability Features – Battery backup, hot spare drives, dual processors, redundant components.
- Management Software – Robust management software makes monitoring and maintenance easier.
Leading hardware RAID manufacturers include Dell PERC, HP Smart Array, Intel RAID, Broadcom MegaRAID, and LSI MegaRAID. Most support a comprehensive set of RAID levels, connectivity options, caching, and monitoring capabilities in their controller lineup.
Choosing Your RAID Level
There is no single “best” RAID type for all scenarios. Choosing the right RAID level involves balancing performance, capacity, and redundancy based on your specific business needs. Some key guidelines include:
- Opt for RAID 0 if maximum performance and storage utilization are critical, but have backups as it lacks redundancy.
- RAID 1 remains a simple option that mirrors two disks for easy redundancy.
- RAID 5 hits the sweet spot for a balance of capacity, performance, and fault tolerance in a typical server.
- Choose RAID 6 when availability is absolutely paramount in large storage arrays.
- Combine striping and mirroring with RAID 10 for transactional databases and high performance applications.
- Consider RAID 6+0 which provides both striping and dual parity for the ultimate combination of speed, capacity, and redundancy.
Also factor in whether hardware or software RAID is most suitable based on your budget, performance needs, and administrative considerations.
Conclusion
Deploying the right RAID solution is an important decision for any storage environment. Matching the RAID level to your availability, performance, capacity, and budget requirements will lead to the ideal setup. RAID 5 offers a versatile option combining good performance and redundancy for many scenarios. RAID 1 mirrors disks for simple redundancy while RAID 10 improves performance through striping and mirroring. For mission critical data, RAID 6 provides the highest level of fault tolerance. Weigh the pros and cons outlined here when architecting a storage system with the appropriate RAID level.