Can you RAID external hard drives?

What is RAID?

RAID stands for Redundant Array of Independent Disks. It is a data storage technology that combines multiple disk drives into a logical unit.1 The main purposes of RAID are to increase data reliability and/or increase input/output performance.2

There are several different RAID levels that each provide specific benefits:3

  • RAID 0: Data is striped across multiple drives for faster performance, but does not provide redundancy.
  • RAID 1: Drives are mirrored for redundancy, but does not improve performance.
  • RAID 5: Data is striped across drives with parity information distributed across all drives for redundancy.
  • RAID 6: Similar to RAID 5 but with double distributed parity for higher fault tolerance.
  • RAID 10: A combination of RAID 1 mirroring and RAID 0 striping for both performance and redundancy.

The RAID level chosen depends on the specific goals such as performance, redundancy, or cost.

Benefits of RAID

RAID offers two key advantages: increased performance and data redundancy (RAID Benefits). By spreading data across multiple disks, RAID can increase read and write speeds, resulting in faster access to data. This is especially beneficial for bandwidth-intensive applications like video editing or data analysis.

RAID also provides data redundancy through techniques like mirroring or parity. If one disk fails, the data can still be accessed from the remaining disks. This protects against catastrophic data loss in the event of a single disk failure. For mission critical data, the redundancy of RAID provides an essential safeguard (RAID Advantages).

Challenges of External HDD RAID

While RAID arrays provide benefits like increased storage capacity, redundancy, and improved performance, using external hard drives in a RAID configuration can pose some unique challenges.

One major drawback is slower speeds. Traditional rotational hard disk drives (HDDs) have slower read/write times compared to internal drives. Combining multiple external HDDs in a RAID can compound this problem, as the RAID is limited by the speed of the slowest drive (Pete Marovich). The connection interface can also bottleneck speeds, especially with older USB standards like USB 2.0.

External HDD RAID arrays may also have compatibility issues. The RAID device drivers need to work properly with the operating system and external interface. Some hardware RAID controllers may not work at all over USB connections. Software RAIDs can be finicky as well if the OS lacks proper driver support.

Finally, device connectivity problems are more likely with external drives that can be accidentally unplugged. This can lead to degraded performance or even data loss if multiple drives disconnect (GRAIDTECH). Careful setup and monitoring is required to prevent issues.

RAID Level Recommendations

When choosing a RAID level for external hard drives, the most common options are RAID 0, RAID 1, RAID 5, and RAID 10.

RAID 0 or disk striping spreads data evenly across multiple drives with no parity or mirroring. It offers fast performance but zero redundancy. According to Microsemi, RAID 0 is best for non-critical storage needs where speed is the priority.

RAID 1 or disk mirroring duplicates data across drives for redundancy. Writes are slower but reads can be faster. RAID 1 provides good performance and protects against single drive failure. As explained on ServerFault, RAID 1 is a common choice for external HDD RAID.

RAID 5 stripes data across drives with distributed parity information. It provides good performance and storage efficiency while protecting against single drive failure. However, Pete Marovich warns that rebuilding a failed RAID 5 array can be slow and stressful for the remaining disks.

RAID 10 combines mirroring and striping for increased performance and redundancy compared to RAID 1 or RAID 0 alone. It protects against multiple drive failures but reduces total capacity. As Microsemi explains, RAID 10 is recommended for setups with 4 or more external hard drives.

Setting up External HDD RAID

Setting up RAID with external hard drives has some specific hardware and software requirements you need to be aware of. First, your computer’s motherboard needs to have RAID capabilities built-in. Many modern motherboards have RAID controllers which allow you to configure RAID arrays in the BIOS. If your motherboard does not support RAID, you will need to purchase a dedicated RAID controller card.

In terms of hard drives, you will need at least two external hard drives of the same capacity. The hard drives should connect via a fast interface like USB 3.0/3.1, Thunderbolt, or eSATA to ensure good performance. The drives themselves should have similar specifications in terms of spindle speed, cache size, etc. Mixing drives with very different specs can cause problems.

For software, you need an operating system that supports RAID configurations. Windows 10 and most Linux distributions include built-in RAID capabilities. The RAID setup is handled through the OS disk management utility or a dedicated software RAID manager. If using Windows, you can access the disk management tool to create RAID arrays.

Overall, setting up external RAID requires RAID-capable hardware and software. Pay close attention to the motherboard chipset, interface speed, and drive specifications when selecting components to ensure optimum compatibility and performance.[1]

Maintenance and Monitoring

Properly maintaining and monitoring an external HDD RAID setup is crucial for ensuring continued protection and availability of your data. Here are some key tips:

Regularly check the RAID status in your RAID software. This will indicate if any drives have failed or have issues. Replace failed drives immediately according to your RAID level – for RAID 1, 5, 6, simply swap out the failed drive. For RAID 0, you will likely need to rebuild the full array.

Periodically run read/write tests on your RAID array to check for bad sectors or other issues. Use built-in tools like chkdsk in Windows or fsck in Linux. Watch for increasing read/write errors as this can indicate a drive failure on the horizon.

Keep spare drives on hand in case of failure. Having a spare drive ready to swap in will minimize downtime. Match the spare’s specs to your existing RAID drives.

Consider staggered drive replacement every 3-5 years as drives age. RAID protects against a single drive failure but does not protect against multiple simultaneous failures. Replacing one drive at a time helps mitigate this risk.

Monitor drive temperatures and enclosure airflow. Excess heat shortens drive lifespan. Use an external RAID enclosure with built-in cooling fans.

Keep firmware and RAID software updated. Updates often contain bug fixes and performance improvements.

Test recovery procedures regularly by restoring from backups. This verifies your data is intact and recovery steps work.


NEVER Use A RAID As Your Backup System!

Performance Optimization

There are several tweaks you can make to optimize the performance of an external HDD RAID array in Windows. According to LaCie (, you should start by formatting the RAID array as NTFS, as this file system is optimized for performance with Windows. Seagate ( also recommends enabling write caching in your hardware settings to allow data to be written faster to the external disks.

You can also go into Device Manager and ensure your external HDD RAID controller is using the latest drivers. Outdated drivers can bottleneck performance. Tweaking your PC’s virtual memory settings can help too – set it to 1.5x your physical RAM for best performance with an external RAID array.

Finally, run the disk defragmentation and optimization utilities in Windows to arrange files efficiently and speed up reads/writes. Schedule defrag to run automatically every week. These tips will ensure your external HDD RAID array performs at its peak.

Data Recovery

Recovering data from a failed RAID array can be challenging, but is possible in many cases. There are a few options for RAID data recovery:

RAID recovery software like EaseUS can scan the disks in the array and rebuild the RAID so you can access the data again. This involves recreating the RAID structure so the data becomes readable. The software scans for file signatures to recover data even if the RAID information is missing or corrupted.

If the RAID is damaged beyond repair, a RAID recovery service may be able to extract the data from the individual disks. They use specialized tools to image the disks and extract files based on file signatures. This can be an expensive option but may work when DIY software fails.

As a last resort, if the RAID disks themselves are physically damaged, you may need a data recovery service to attempt extracting data from the disk platters themselves. This is a complicated and expensive process with no guarantee of success.

To avoid data loss, be sure to backup your RAID array regularly. Test restoring from backups periodically to verify they are valid. With good backups, RAID data recovery becomes less crucial.

Alternative Options

While RAID is a popular method for protecting data across multiple hard drives, there are other redundancy options besides RAID for external hard drives that may better suit some users’ needs. According to an article on Reddit (, one alternative is using an rsync script to backup files to a USB hard drive. This copies new files and only replaces those that have changed, reducing redundancy.

Another option is to use backup software that supports versioning. This allows multiple versions of files to be retained over time, acting as a safeguard against accidental changes or deletions. Some backup tools like Apple Time Machine have built-in versioning capabilities. Setting up scheduled backups to alternate external drives can also provide redundancy without RAID.

For users who only need occasional backups or don’t need frequent access to the data, cloud storage services like Dropbox, Google Drive, or Microsoft OneDrive allow files to be accessed from multiple devices and provide some data protection. Though not as fast as local external storage, cloud backups can serve as an alternative to RAID.

Using a mirrored folder syncing utility is another way to redundantly backup files without full RAID. Free options like FreeFileSync allow users to mirror the contents of one folder to another external drive in real time or on a schedule.

Ultimately, the ideal solution depends on performance needs, budget, and the importance of protecting against different data loss scenarios. Non-RAID options provide more flexibility but less redundancy than full RAID configurations.


In summary, RAID external hard drives have both benefits and challenges. On the positive side, RAID offers redundancy to protect data and can improve performance. However, it also comes with added complexity and cost. RAID Level 1 is generally the best option for external drives since it offers mirroring for fault tolerance while still providing good performance.

For home users needing basic data protection, a single external drive with regular backups may be sufficient. But for those requiring maximum uptime and ability to survive drive failures, RAID 1 or 5 on external drives is a worthwhile investment. Just be prepared to spend more upfront and understand the setup and maintenance required.

In the end, evaluate your specific needs and environment. RAID external hard drive arrays provide excellent redundancy and speed for the right situations. But they require hardware, configuration and some IT expertise to implement properly. Consider both the pros and cons before deciding if RAID is right for your external storage needs.