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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →The ServeTheHome RAID calculator gives an approximate usable-capacity estimate for a selected RAID layout and drive configuration. Use it to compare how mirroring and parity change available space, then verify formatted capacity, fault tolerance, performance, and hardware compatibility separately.
What the ServeTheHome RAID calculator does
ServeTheHome describes its free tool as a “version 1 RAID calculator” that calculates “approximate array sizes.” Its purpose is to show the usable capacity of different configurations, such as RAID 1 or RAID 60. The page also points readers to a separate reliability calculator for data-loss estimates; this capacity tool should not be treated as a reliability, performance, backup, or purchasing analysis.
The embedded widget’s current input fields, supported RAID levels, mixed-drive rules, and output units are not documented in the page text. Check the live calculator before assuming that it supports a particular layout or combination of drive sizes.
How RAID layout changes usable capacity
Redundancy consumes raw capacity. These are common planning rules for arrays built from same-size drives:
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- 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.
| RAID level | Typical usable-capacity rule | What consumes capacity |
|---|---|---|
| RAID 0 | Total capacity of all drives | No redundancy |
| RAID 1 | Capacity of one drive | A mirrored copy |
| RAID 5 | Total capacity minus one drive | One drive’s worth of parity |
| RAID 6 | Total capacity minus two drives | Two drives’ worth of dual parity |
| RAID 10 | About half of total capacity | Mirrored pairs, then striping |
These formulas are simplified planning rules, not guarantees that every controller, software implementation, or mixed-size arrangement behaves identically. Drive count, the smallest member size, metadata, and implementation-specific reservations can affect the result.
Worked capacity examples
Eight 8 TB drives in RAID 5
Western Digital’s RAID capacity calculator gives 8 × 8 TB in RAID 5 as 56 TB usable (56,000 GB). One 8 TB drive’s equivalent capacity is reserved for parity, leaving seven drive-equivalents for data.
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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
Eight 4 TB drives across common levels
The same Western Digital calculator compares an eight-drive set as follows:
| Layout | Illustrative usable capacity |
|---|---|
| RAID 0 | 32 TB |
| RAID 5 | 28 TB |
| RAID 6 | 24 TB |
| RAID 10 | 16 TB |
These are worked calculator examples, not results from a named study or a benchmark.
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- 【Reliable External Storage System for Individuals and business】The 3.5 hard drive enclosure supports 2.5/3.5 inches HDD and SSD, max capacity up to 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.
- 【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.
Usable array capacity is not the same as free space in the operating system
RAID capacity is the array’s logical size before an operating system and file system format it. Western Digital cautions that the reported formatted capacity depends on the operating system and file system. Decimal drive labels also differ from binary reporting: manufacturers use 1 TB for one trillion bytes, while an operating system may display a 4 TB drive as roughly 3.64 TB in binary units.
- Raw capacity: the sum of the capacities printed on the drives.
- Usable RAID capacity: the space left after mirroring or parity overhead.
- Formatted capacity and free space: what remains after file-system metadata, reserved space, snapshots, and stored data.
Keep TB (decimal) distinct from TiB (binary) when sizing a volume or comparing a calculator result with an operating-system display.
Rank #4
- !!!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.
- 【Reliable External Storage System for Individuals】The 3.5 hard drive enclosure supports 2.5/3.5inches HDD and SSD , max capacity up to 160TB( 20TB for each hard drive), Not compatible with WD 20TB hard drives, but supports Seagate 20TB hard drives.it's a ideal external hard drive enclosure for personal or enterprise using.Save space on your desktop or laptop.
- 【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.
A practical way to use the calculator
- List the intended drives. Record the number and rated capacity of each member. Do not assume mixed-size support until the current tool and your RAID implementation document it.
- Select the RAID level. Compare at least the layouts that meet your redundancy and performance requirements; capacity alone does not establish how many failures an array can tolerate.
- Record the displayed result and units. Note whether the widget reports TB, GB, TiB, or another unit.
- Allow for formatting and operational headroom. The eventual file-system volume will not necessarily show the calculator’s full logical number.
- Validate the design elsewhere. Check controller or operating-system support, rebuild behavior, workload performance, backup coverage, and the manufacturer’s current drive guidance before purchasing.
What the calculator cannot answer by itself
Reliability and failure tolerance
A larger usable number does not prove greater safety. RAID 0 has no redundancy, while parity and mirrored layouts have different failure limits and rebuild characteristics. Use a reliability-focused analysis and maintain an independent backup rather than inferring data-loss risk from capacity.
Performance
Read and write speed depends on the RAID implementation, controller or software stack, workload, cache, network, and drive type. The ServeTheHome capacity page does not present performance estimates.
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- [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
Mixed-size and implementation behavior
Simple formulas assume comparable drive sizes. Many implementations base each member on the smallest drive, and some layouts impose minimum drive counts or other restrictions. Confirm those rules for your NAS, controller, or operating system.
Final volume size
Partition tables, file-system metadata, snapshots, thin provisioning, and reserved space can reduce the capacity available for files after the array is created.
Choosing drives after estimating capacity
Drive selection depends on the enclosure, interface, workload, vibration environment, endurance requirements, and support policy. Western Digital categorizes WD Red Plus and WD Red Pro for NAS arrays, and WD Gold and Ultrastar for enterprise and data-center arrays. Those categories indicate intended environments, not a universal recommendation for every system; check the specific model’s compatibility and workload specifications.
Bottom line
Use the ServeTheHome calculator for a quick, approximate comparison of RAID usable space. Treat its result as the array’s planning capacity, convert units carefully, and then verify implementation limits, formatted volume size, reliability, performance, backups, and drive suitability before committing to a design.
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