With so many options for hard drives on the market, choosing the right ones for a RAID setup can be tricky. This comprehensive guide will walk you through everything you need to consider when selecting hard drives for RAID.
What is RAID?
RAID stands for Redundant Array of Independent Disks. It is a data storage technology that combines multiple disk drive components into a logical unit. Data is distributed across the drives in one of several ways called RAID levels, depending on the required level of redundancy and performance.
The different RAID levels include:
- RAID 0: Stripes data across drives for faster performance, but does not provide redundancy.
- RAID 1: Mirrors data across drives for redundancy.
- RAID 5: Stripes data across drives with parity information distributed across drives to allow for single drive failure without data loss.
- RAID 6: Similar to RAID 5 but can withstand the failure of two drives.
- RAID 10: Mirrors data and stripes the mirrors.
RAID aims to provide increased storage performance, capacity, and reliability through redundancy. If a drive fails, the data can still be accessed from the other drives. RAID improves performance by allowing simultaneous access to data across multiple drives.
Hard drive factors for RAID
There are several factors to evaluate when selecting hard drives for a RAID configuration:
Drive interface
This determines the connection between the drive and computer. Common options include:
- SATA – Serial ATA is the most popular interface for consumer drives. Provides good speeds up to 6Gbps.
- SAS – Serial Attached SCSI is found in enterprise drives. Offers faster speeds up to 12Gbps.
- NVMe – Designed for SSDs. Very high speeds over PCIe bus.
For RAID, matched drives with the same interface is recommended. NVMe is best for all SSD RAID. SATA works for HDDs or mixed HDD/SSD RAID. SAS for enterprise configurations.
Drive capacity
The storage capacity of each drive depends on your total storage needs. For optimal performance, all drives in the RAID array should have the same capacity. If not, there will be unused space on larger drives.
Typical capacities are:
- 2-4TB for HDD RAID
- 240-480GB for SATA SSD RAID
- 400GB-3TB for NVMe SSD RAID
Drive RPM
This indicates the rotational speed of mechanical hard disk drives (HDDs) measured in revolutions per minute (RPM). Common speeds include:
- 5400 RPM – Slowest, least expensive drives
- 7200 RPM – Offer better performance
- 10,000-15,000 RPM – Fast enterprise-class drives
For RAID, matching the RPM provides optimal performance. 7200 RPM or faster drives recommended for RAID configurations seeking better speed.
Drive cache
The cache is high speed memory built into the drive to buffer reads and writes. More cache can improve RAID performance. Cache sizes typically range from 16MB to 256MB for mechanical HDDs. SSDs have levels of 100GB or more.
Drive workload rating
This specifies how much constant writing a drive is designed for over its lifetime – measured in drive writes per day (DWPD). Consumer drives are typically rated for 1 DWPD. Drives meant for RAID are rated for higher workloads like 2-10+ DWPD.
RAID hard drive factors by level
The RAID level you choose will determine the ideal drive specifications…
RAID 0
RAID 0 seeks maximum performance by striping data across drives. Key considerations include:
- Interface – NVMe SSD provides fastest access
- Capacity – Larger drives store more data
- RPM or IOPS – Faster rotational speed or I/O operations per second
- Workload – Higher DWPD ratings handle heavy workloads
RAID 0 does not provide fault tolerance since data is split across drives. Use enterprise class drives designed for heavy workloads.
RAID 1
RAID 1 creates an exact copy of data on a second drive for redundancy. Important factors are:
- Capacity – Drives must be same size
- Interface – Matched connections
- RPM or IOPS – Matched performance
Use drives from the same model line with identical specs for optimal RAID 1 performance.
RAID 5
RAID 5 stripes data across drives and adds parity information. Key considerations:
- Capacity – All drives should have same capacity
- Interface – Same interfaces
- RPM or IOPS – Matching performance
- Workload – Higher workload ratings
At least 3 drives required for RAID 5 but more drives provide better performance. Enterprise class drives recommended.
RAID 6
RAID 6 is similar to RAID 5 but offers fault tolerance up to two drive failures. Guidelines include:
- Capacity – Matched drive sizes
- Interface – Same interfaces
- RPM or IOPS – Matching specs
- Workload – Choose drives rated for 24/7 operation
Minimum 4 drives needed for RAID 6. More drives offer better performance. Target enterprise class HDDs or SSDs.
RAID 10
RAID 10 provides redundancy through mirroring while also striping data. Ideal drive features:
- Capacity – All drives must have same capacity
- Interface – Consistent interfaces
- RPM or IOPS – Matching performance metrics
Minimum of 4 drives required. Performance optimized by using faster RPM HDDs or SSDs.
Enterprise vs. consumer hard drives
Enterprise class drives are engineered for 24/7 operation and RAID environments. They offer:
- Higher workload ratings – Built to handle constant activity
- Lower failure rates – More reliable with a longer lifespan
- Faster performance – Optimized for heavy workloads
- Advanced features – Things like TLER for better RAID recovery
- Longer warranties – Typically 5 years or more
However, enterprise drives also have a higher cost. Consumer HDDs can be used in RAID configurations for home or small business use to save money.
Enterprise HDD recommendations
- Seagate Exos X Series – Designed for 24/7 RAID
- Western Digital Gold Series – Optimized for RAID
- Toshiba MG Series – Built for mission-critical storage
Consumer HDD options
- Seagate Barracuda – Cost-effective performance
- Western Digital Blue – Solid budget choice
- Toshiba P300 – Affordable high capacity
SSD vs. HDD for RAID
SSDs provide better performance than HDDs but at a higher price point. Key differences:
| SSD | HDD |
|---|---|
| No moving parts – more resilient | Mechanical parts prone to failure |
| Much faster read/write speeds | Slower performance due to physical platters |
| Silent operation | Audible noise from spinning platters |
| Typically more expensive per GB | Lower cost per GB of storage |
| Lower capacity options | Higher capacities available |
| Consume less power | HDDs use more power |
SSDs provide faster speeds, lower latency, silent operation and resilience against shocks/vibration. But HDDs can offer larger capacities for less cost.
When to use SSDs for RAID
SSDs make sense for RAID configurations where performance is the priority. Examples include:
- Transactional databases needing fast access
- Virtualized environments
- High performance computing
- Video editing or render farms
The higher cost of SSDs may be justified by the speed boost compared to HDD RAID.
When to use HDDs for RAID
HDD-based RAID can be a good choice when:
- You need lots of affordable storage capacity
- Data access speed is less important
- Budget constraints make SSDs too expensive
HDDs deliver more storage space per dollar but sacrifice performance. They work well for backup storage or archival data.
Buy more disks than you need
It’s a good idea to buy at least one or two extra hard drives than the minimum required for your planned RAID setup. This provides spare drives in case of failures. Hot spares can automatically rebuild a RAID array in case of a failed drive.
Having spare disks on hand avoids downtime if a drive fails and needs to be replaced. Purchasing more drives upfront reduces the chance of scrambling to source a compatible replacement.
Use a hardware RAID controller
A dedicated RAID controller handles the processing required to manage the RAID array. Benefits include:
- Frees up system resources
- Provides caching to boost performance
- Adds extra reliability with a battery backup
- Enables more advanced RAID management
Software RAID relies on the system’s CPU and has limited capabilities. For large or mission critical arrays, a hardware RAID controller is recommended.
RAID controller features
- RAID levels supported
- Drive interface connections
- Cache memory size
- Battery backup module
- Management software
Popular hardware RAID controller options include:
- LSI MegaRAID – Enterprise grade controllers
- Dell PERC – Made for Dell servers
- HP Smart Array – Designed for HP servers
- Areca – High performance with SSD caching
Match drive specs for best results
For a reliable, high performance RAID array:
- Use enterprise class drives designed for RAID
- Choose drives with matched capacities, interfaces, RPM/IOPS
- Include hot spares to protect against disk failures
- Consider a hardware RAID controller for large or critical arrays
Carefully matching up drives optimizes speed, consistency and redundancy in your RAID configuration. Paying attention to workload ratings, warranties and RAID-specific features also helps build a robust storage solution.
Conclusion
Constructing a RAID array requires choosing compatible hard drives that fit your performance and capacity requirements. Enterprise class drives built for RAID offer reliability and workload ratings needed for optimal results. For budget arrays, consumer drives can work if matched in specs. SSDs provide speed while HDDs offer affordability and high capacities.
Matching drives in interface, RPM/IOPS, and capacity is advised to prevent wasted resources or bottlenecks. Including hot spares protects against downtime if failures occur. For mission critical RAID, invest in a dedicated hardware controller for best performance and advanced management capabilities.
With the right drives for your workload and proper RAID implementation, you can build fast, resilient storage that takes advantage of the benefits of RAID – improved speed, capacity, and availability through redundancy.