What Is a RAID Storage Calculator?
A RAID storage calculator helps you determine how much usable disk space you will get from a RAID (Redundant Array of Independent Disks) configuration before you purchase drives or build your server. RAID combines multiple physical disks into a single logical unit for improved performance, redundancy, or both, but each RAID level uses your raw storage differently.
Without a calculator, figuring out the actual usable capacity requires understanding the specific formulas for each RAID level, factoring in parity overhead, mirroring costs, and minimum disk requirements. This tool does all that math instantly so you can compare every standard RAID level side by side and make an informed decision about your storage architecture.
Whether you are building a home NAS, configuring a file server, planning enterprise storage, or setting up a media production workstation, knowing the real-world usable capacity before committing to hardware saves both money and time. The calculator covers RAID 0, 1, 5, 6, and 10, which are the most widely deployed configurations in both consumer and enterprise environments.
Use this calculator to answer questions like: How many terabytes of usable space will I get with 8 drives in RAID 6? What is the storage efficiency difference between RAID 5 and RAID 10? How many drives do I need for a specific usable capacity target?
RAID Level Comparison
Each RAID level makes different trade-offs between storage capacity, data protection, and read/write performance. Here is what each level offers:
**RAID 0 (Striping)** splits data across all disks with no redundancy. You get the full combined capacity and the fastest read/write speeds, but if any single disk fails, all data is lost. RAID 0 is best suited for temporary scratch disks, video editing caches, or any scenario where performance matters more than data safety.
**RAID 1 (Mirroring)** writes identical copies of data to every disk in the array. You only get the capacity of a single disk regardless of how many drives you use, but you can lose all but one drive without data loss. RAID 1 is commonly used for operating system drives and critical databases where uptime is paramount.
**RAID 5 (Striping with Single Parity)** distributes parity information across all disks, dedicating the equivalent of one disk's worth of space to parity. This provides a good balance: you lose only one disk worth of capacity while gaining protection against a single disk failure. RAID 5 is one of the most popular configurations for general-purpose file servers and NAS devices.
**RAID 6 (Striping with Double Parity)** is similar to RAID 5 but uses two disks' worth of parity, allowing the array to survive two simultaneous disk failures. This extra safety comes at the cost of slightly more overhead and slower write performance. RAID 6 is recommended for large arrays where the time needed to rebuild a failed drive increases the risk of a second failure.
**RAID 10 (Mirrored Stripes)** combines RAID 1 mirroring with RAID 0 striping. Data is mirrored in pairs, and the pairs are striped for performance. You get half the raw capacity as usable space, excellent read/write performance, and protection against at least one failure per mirror pair. RAID 10 is favored for database servers and applications requiring both high throughput and reliability.
How RAID Capacity Is Calculated
The usable capacity of a RAID array depends on the number of disks (N), the size of each disk, and the RAID level. All disks in a RAID array should be the same size; if they are not, the array typically uses only the capacity of the smallest disk from each drive.
**Formulas:** \`\`\` RAID 0: Usable = N x Disk Size RAID 1: Usable = 1 x Disk Size RAID 5: Usable = (N - 1) x Disk Size RAID 6: Usable = (N - 2) x Disk Size RAID 10: Usable = (N / 2) x Disk Size \`\`\`
**Storage Efficiency** is the percentage of raw capacity that becomes usable space: \`\`\` Efficiency = (Usable Capacity / Total Raw Capacity) x 100 \`\`\`
For example, with 6 disks of 4 TB each (24 TB raw): - RAID 0 gives 24 TB usable (100% efficiency) - RAID 1 gives 4 TB usable (16.7% efficiency) - RAID 5 gives 20 TB usable (83.3% efficiency) - RAID 6 gives 16 TB usable (66.7% efficiency) - RAID 10 gives 12 TB usable (50% efficiency)
**Minimum Disk Requirements:** - RAID 0 and RAID 1: 2 disks minimum - RAID 5: 3 disks minimum - RAID 6 and RAID 10: 4 disks minimum - RAID 10 also requires an even number of disks
How to Use This Calculator
1. Enter the number of physical disks you plan to use in your RAID array (between 2 and 24). 2. Select the size of each individual disk from the dropdown, or choose "Custom size" to enter a specific capacity in terabytes. 3. View the instant comparison of all RAID levels showing usable capacity, storage efficiency, parity overhead, and fault tolerance. 4. Check the highlighted hero result for the most commonly recommended configuration (RAID 5 when available). 5. Review the detailed breakdown cards to see which RAID levels are available with your disk count and which are not. 6. Use the bar chart to visually compare usable capacity across all available RAID levels.
FAQs
Q: What RAID level should I use? A: It depends on your priorities. For maximum performance with no data protection, use RAID 0. For the best balance of capacity and single-disk fault tolerance, RAID 5 is the most popular choice. For critical data requiring extra protection, use RAID 6 or RAID 10. RAID 1 is ideal when you need maximum redundancy and the simplest recovery process.
Q: Does RAID replace backups? A: No. RAID protects against disk hardware failures, but it does not protect against accidental deletion, file corruption, ransomware, controller failures, fire, theft, or other disasters. You should always maintain separate backups of important data, ideally following the 3-2-1 backup strategy (3 copies, 2 different media types, 1 offsite).
Q: Can I mix different disk sizes in a RAID array? A: Technically yes, but the array will only use the capacity of the smallest disk from each drive. For example, mixing a 4 TB and an 8 TB drive in RAID 1 gives you only 4 TB of usable and 4 TB of mirrored space, wasting 4 TB on the larger drive. For best results, always use identical disks.
Q: What happens when a RAID 5 disk fails? A: The array continues to operate in a degraded state using parity data to reconstruct the missing disk's information on the fly. Performance decreases during this period. You should replace the failed disk as soon as possible and rebuild the array. During the rebuild, if a second disk fails, all data is lost because RAID 5 can only tolerate one failure.
Q: Is RAID 10 better than RAID 5? A: RAID 10 offers better write performance and faster rebuilds because it only needs to copy data from the surviving mirror rather than recalculate parity across all disks. However, RAID 10 uses 50% of your raw capacity for redundancy, while RAID 5 uses only one disk's worth. Choose RAID 10 for databases and high-write workloads, and RAID 5 for general file storage where capacity efficiency matters more.
Q: Why does RAID 10 require an even number of disks? A: RAID 10 works by creating mirrored pairs of disks and then striping across those pairs. Each pair consists of exactly two disks, so the total must be even. With an odd number of disks, you cannot form complete mirror pairs.
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