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RAID 5 stripes data and distributed parity across at least three drives, using the equivalent of one drive for redundancy. It can reconstruct data after one drive fails, but a second failure before rebuild completes can destroy the array. RAID 5 is therefore a capacity-efficient choice for many sequential or read-heavy workloads—not a backup and not automatically the best option for critical or write-intensive data.
How RAID 5 works
RAID 5 divides files into blocks and stripes those blocks across all member drives. Parity blocks are distributed among the drives rather than stored on one dedicated parity disk. If a drive fails, the controller or software combines the surviving data and parity to calculate the missing contents. Replacing the failed drive lets the array rebuild its lost redundancy.
Intel describes the mechanism this way: “Parity is a mathematical method for re-creating data that was lost from a single drive, which increases fault tolerance.” (Intel, Defining RAID Volumes for Intel® Rapid Storage Technology)
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Minimum and supported drive counts
The Intel Rapid Storage Technology and QNAP QTS implementations documented for this article require at least three drives. QNAP’s QTS 5.2.x documentation lists RAID 5 support for three to 16 drives; other NAS and controller products can impose different limits, so check the exact model documentation before buying drives. (QNAP QTS 5.2.x RAID types)
#1 Best Overall
- Note:The eSATA port on this product does not support the use of a computer’s SATA-to-eSATA adapter. Hot-swapping is not supported. The computer’s eSATA port must support RAID functionality to properly access multiple drive bays via the eSATA port; otherwise, only one drive bay can be accessed.
- 【Reliable External Storage System for Individuals】The 3.5 hard drive enclosure supports 2.5/3.5 inches HDD and SSD , max capacity up to 80TB( 20TB for each hard drive), it's a ideal external hard drive enclosure for personal or enterprise using.Save space on your desktop or laptop.
- 【No heat,】The 4 bay hard drive reader built in Aluminum-Alloy materials and 2 inch Fans.Maximize the security of your data.NOTE：Fan noise is around 40-50 decibels, not recommended if you are very sensitive to noise.
- 【8 Raid Modes】This external hdd raid enclosure supports RAID 0/1/3/5/10, CLONE, LARGE, NORMAL.NOTE:When replacing RAID, you need to go back to NORMAL and set the desired RAID mode.Designing RAID may result in data loss.MAC OS no Raid software. Raid Mode Switching Method Disconnect the power, use a screwdriver, toggle the paddle to the corresponding mode, press and hold the reset button, turn on the power, hold reset for ten seconds, the raid mode will be successfully switched.
- 【Up to 5Gbps】This raid enclosure equips with JMS567+JMB393 chip and USB 3.0, eSATA output interface.
The capacity formula
Usable capacity is approximately the capacity of the smallest drive multiplied by one less than the number of drives:
Usable RAID 5 capacity ≈ smallest drive capacity × (number of drives − 1)
For example, four equal-capacity 8 TB drives provide roughly 24 TB before filesystem, metadata and implementation overhead. If one drive is smaller, the array generally bases every member’s contribution on that smallest capacity. QNAP recommends matching drive brand, type and capacity for better space efficiency and performance; that recommendation is specific to QNAP’s guidance, while the smallest-drive limitation is the broader RAID 5 rule.
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- High Speed Data Transmission: The D2-320 hard drive enclosure (a DAS, NOT a NAS) adopts USB 3.2 Gen2 protocol for high-speed data transmission up to 10Gbps. With 2 hard drives in RAID 0, the read/write speed can reach up to 521MB/s (SATA III HDD 8TB x 2). With 2 SSD's in RAID 0, the read speed can reach 1075MB/s (SATA III 1TB SSD x 2)
- Multiple RAID Configurations: The D2-320 is a hardware RAID enclosure and it supports RAID 0, RAID 1, JBOD and SINGLE which can better satisfy various demands of users. In RAID 1, data will be in a mirror backup. When there is a damaged hard drive, you can directly replace the hard drive, and the data will be recovered automatically. This provides an absolute security for the data
- Super-Large Storage Capacity: The D2-320 USB storage enclosure can support up to two 3.5" and 2.5" SATA HDD, as well as 2.5" SATA SSD, with a maximum capacity of 22TB per drive, providing users with up to 44TB (22TB x 2) of storage space
- Intelligent Temperature Control: The D2-320 HDD enclosure has an intelligent temperature-controlled and low-noise fan that automatically adjusts its speed based on the temperature of the hard disk. This feature ensures that the hard disk operates at its best temperature and provides better heat dissipation
- Tool-Free Hard Drive Installation: The D2-320 external hard drive enclosure features a tool-free hard drive tray design that allows for easy installation and removal of hard drives without the need for any tools. Furthermore, the D2-320 incorporates a brand new Push-lock unique design from TerraMaster, which automatically locks the hard drive tray when you insert the hard drive, preventing the hard drive from falling out or disconnecting
Failure tolerance and rebuild exposure
One failed drive
RAID 5 is designed to tolerate one failed drive per array. The array can continue operating in a degraded state while the missing data is reconstructed from the remaining drives and parity. Performance and redundancy are reduced during this period.
A second failure
Once one drive has failed, RAID 5 has no remaining single-drive margin. Seagate warns that a second drive failure before the rebuild finishes loses the array’s data. Rebuild time and exposure depend on drive size, drive condition, controller or NAS software, background workload and the implementation’s rebuild policy. (Seagate RAID Manager: RAID levels)
Monitor array health, keep a tested replacement drive available, and investigate SMART warnings or read errors promptly. A rebuild restores redundancy; it does not restore files that were deleted or corrupted before the drive failure.
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- 【4 Raid Modes】!!!NOTE:Press and hold the "Reset" button for 5 seconds after reset the RAID array!!!This raid enclosure supports 4 RAID Modes(RAID 0, RAID 1, Normal, JBOD).Designing RAID may result in data loss.MAC OS no Raid software.
- 【No heat】The 2 bay hard drive reader built in Aluminum-Alloy materials and 2 inch Fan.Maximize the security of your data.NOTE：Fan noise is around 40-50 decibels, not recommended if you are very sensitive to noise.
- 【Up to 5Gbps】This dual bay raid enclosure equips with JMS561 chip and USB 3.0 output interface.
- 【Wide Compatibility, Plug and Play】Equipped with USB A/C 3.0 Cable.Compatible with Windows 7 and above, Mac 9.1 and above, Linux.Plug and play, no fuss, no muss.
RAID 5 performance
Reads
Because data is striped, multiple drives can service read requests concurrently. Intel states that RAID 5 read performance can exceed that of a single drive. Actual results depend on drive count and type, controller or software implementation, cache, firmware and request pattern. (Intel documentation)
Writes
Writes are less straightforward. For many partial-stripe writes, the system must read existing data and parity, calculate new parity, and write the updated blocks. Large full-stripe writes, a capable controller and write-back caching can change the balance, but parity work means RAID 5 does not deliver the same simple write scaling as a non-parity stripe.
Intel notes that writes do not receive the same benefit as reads because parity must be calculated and written. If Intel RST’s optional RAID 5 write-back cache is enabled, Intel recommends using a UPS; that is a condition for that feature, not a universal RAID 5 requirement.
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- !!!NOTE:When the 8-bay enclosure being used, there is at least one hard drive must be inserted into HDD1-HDD4, same goes for HDD5-HDD8, 2 HDDs is a minimun quantity to be inserted.Please read the instructions carefully before trying!!!Be sure to save a good backup of your data before setting up RAID, which will format your hard drive after setting up RAID!!!!!!
- NOTE: When using this product, please first confirm that the hard drive loaded into this product is normal, otherwise it will lead to not out of the drive, such as loading more than one hard drive, it will only show one, can not confirm which one is bad, please load a hard drive, power on, out of the drive a, confirm that it is normal, turn off, and then load the second, in the power on, out of the drive two, to confirm that it is normal, and so on, one by one to load, until you find the The problematic hard drive. For example, if there is a problem with one of the 8 hard drives, only one drive will come out.
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- 【8 Raid Modes】This external raid enclosure supports CLONE, LARGE/ LARGE*2, NORMAL, RAID0*2, RAID5*2, RAID50, RAID00. NOTE:When replacing RAID, you need to go back to NORMAL/PM10 and set the desired RAID mode.Designing RAID may result in data loss. !!!Raid Mode Switching Method!!! Disconnect the power, use a screwdriver, toggle the paddle to the corresponding mode, press and hold the reset button, turn on the power, hold reset for ten seconds, the raid mode will be successfully switched.
- 【No heat】The 8 bay hard drive reader built in Aluminum-Alloy materials and two 2.9 inch Fans.Maximize the security of your data. NOTE：Fan noise is around 40-50 decibels, not recommended if you are very sensitive to noise.
Degraded operation and rebuilds
During a failure and rebuild, the system must calculate missing data while serving normal requests and writing reconstructed blocks. Intel reports reduced write performance during rebuild. Do not apply a fixed speed percentage or rebuild duration to every array: no single benchmark covers all combinations of disks, controller, firmware and workload.
For one product-specific comparison, Dell characterizes PowerVault ME5 RAID 5 as offering good sequential I/O, good random-read I/O and moderate random-write performance, with stated use cases including big data, media and entertainment ingest, broadcast and past production. Those ratings describe Dell’s ME5 implementation, not a guarantee for every NAS or controller. (Dell PowerVault ME5 RAID selection)
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| Level | Drive-failure tolerance | Approximate usable capacity | Typical trade-off |
|---|---|---|---|
| RAID 5 | One drive | Smallest drive × (number of drives − 1) | Good capacity efficiency and read/sequential behavior; parity makes writes and rebuilds more demanding. |
| RAID 6 | Two drives | Smallest drive × (number of drives − 2) | More protection during long rebuild windows, at the cost of two drives’ capacity and additional parity work. |
| RAID 10 | At least one failure in each affected mirror pair; the result depends on which drives fail | About half of combined raw capacity | Excellent random-read and random-write potential, but lower usable capacity. |
QNAP describes RAID 6 as a two-disk-failure-tolerant level suited to critical, business and general storage. It describes RAID 10 as providing excellent random read/write speeds and recommends it for high-random-access workloads such as databases. These are vendor recommendations, so validate them against your controller, drive set and workload. (QNAP RAID types)
Best Value
- [Flexible RAID Mode Management]: This 3.5-inch RAID HDD enclosure supports eight configuration modes, namely 0, 1, 3, 5, 10, JBOD, CLONE, and CLEAR. It enables dual data backup, enhances data security, and caters to the individualized needs of diverse users. Note: It is advisable to back up your data before mode switching. If you have any inquiries, please do not hesitate to contact us
- [Supports 22TB Single Disk]: The 5-bay HDD enclosure accommodates 3.5-inch SATA disks, and the maximum storage capacity amounts to 110TB. It can effortlessly fulfill the storage requirements of large-scale engineering projects, high-resolution video footages, and other large-capacity data, eliminating concerns about capacity shortages
- [5Gbps Data Transfer]: The USB 3.0 interface of the external hard drive bay is compatible with SATA 6 Gbps, and the transfer speed reaches up to 235MB/s, facilitating effortless backup and transfer of files and videos, enabling centralized management and enhancing work efficiency
- [Effective Heat-dissipation]The 3.5-inch aluminum HDD case is outfitted with an 80mm silent cooling fan. Front and rear vents are designed, and the airflow effectively dissipates heat, ensuring the stable and efficient operation of the equipment over an extended period
- [Safety Protection]: The RAID enclosure features a bracket-free design for quick disassembly and assembly and possesses an independent safety locking mechanism to effectively prevent the unexpected removal or loss of the hard disk and guarantee the security of data
When RAID 5 makes sense
- Capacity matters: you want to reserve roughly one drive’s capacity for parity rather than two drives (RAID 6) or half the array (RAID 10).
- The workload is read-heavy or sequential: file serving, media ingest and similar patterns can align with the qualitative performance descriptions above.
- Your rebuild exposure is acceptable: you can monitor the array, replace a failed drive quickly and tolerate reduced performance during rebuild.
- The implementation supports it: the NAS or controller has enough bays, lists the intended drive types and capacities as compatible, and documents RAID 5 behavior for your firmware version.
When to choose another level
Choose RAID 6 when a second failure during rebuild is unacceptable
RAID 6 consumes capacity equivalent to two drives but maintains protection against two failed drives. It is often the safer choice for critical data, larger arrays or situations where replacing and rebuilding a failed drive may take substantial time.
Choose RAID 10 for demanding random access
Databases, virtual-machine storage and other write-heavy random workloads may benefit from RAID 10’s mirrored layout. You give up about half of raw capacity, and two failures can still be fatal if they occur in the same mirror pair, so confirm the controller’s layout and monitoring behavior.
Use a non-RAID design when availability is not the priority
For a single disk, independent disks or a replicated storage system, RAID may add complexity without solving the actual requirement. Choose based on recovery objectives, application behavior and the number of independent copies you can maintain.
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RAID is not a backup
RAID’s documented protection is against a drive failure inside the array. It does not create an independent, recoverable copy after accidental deletion, malware, silent corruption, theft, fire, or loss of the entire enclosure. Maintain separate backups, keep at least one copy outside the array, and test restoration. A backup plan remains necessary whether the array uses RAID 5, RAID 6 or RAID 10.
Quick Recap
A practical RAID 5 decision checklist
- Confirm the NAS or controller’s supported RAID levels and drive-count range for the exact firmware or software version.
- Calculate capacity using the smallest drive, then reserve space for filesystem overhead and growth.
- Measure or characterize the workload: sequential versus random, read versus write, and normal versus rebuild conditions.
- Decide whether one-drive tolerance is sufficient for the time required to source and rebuild a replacement.
- Compare RAID 5 with RAID 6 and RAID 10 using the capacity and failure-tolerance trade-offs in the table.
- Prepare monitoring, replacement-drive compatibility and independent backups before placing important data on the array.
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