RAID Calculator

Q: How many drives do I need for RAID 5?

You need at least 3 drives for RAID 5. One drive's worth of space is used for parity data, so with 3 drives you get the usable capacity of 2. More drives means more usable space, but you always lose one drive's worth to parity.

Q: What happens to my storage when I use mixed drive sizes in RAID?

Most RAID levels use the smallest drive's size for every drive in the array. If you mix a 2 TB drive with two 4 TB drives, the array treats all three as 2 TB drives. The extra space on the larger drives is wasted. The calculator shows this unused space in gray on the capacity bar.

Q: Why does my drive show less space than the label says?

Drive makers use decimal math where 1 TB equals 1,000 GB. Your computer uses binary math where 1 TiB equals 1,024 GiB. That difference means a drive labeled 1 TB shows up as about 931 GiB in your operating system. Use the Binary option under Advanced Options to see sizes the way your OS reports them.

Q: What does storage efficiency mean?

Storage efficiency is the percentage of your total raw drive space that you can actually use for files. For example, if you have 16 TB of raw capacity and 12 TB is usable after RAID overhead, your storage efficiency is 75%. Higher efficiency means less space lost to protection.

Q: Which RAID level gives the most usable space?

RAID 0 gives 100% of your total drive space because it has no redundancy at all. However, if any single drive fails, you lose everything. Among RAID levels that offer protection, RAID 5 gives the most usable space because it only uses one drive's worth for parity.

Q: What does fault tolerance mean in this calculator?

Fault tolerance is the number of drives that can break at the same time without losing your data. For example, RAID 5 can survive 1 drive failure and RAID 6 can survive 2. RAID 0 has zero fault tolerance, so any single drive failure destroys the whole array.

Q: What are the read and write speed multipliers?

These numbers show how much faster the array is compared to a single drive . A read multiplier of 4× means the array can read roughly four times faster than one drive alone. These are theoretical maximums. Real-world speeds depend on your RAID controller, drive type, and workload.

Q: What is a RAID rebuild and why does it matter?

A rebuild happens when a failed drive is replaced and the array reconstructs the missing data onto the new drive. During a rebuild, the array is slower and more vulnerable. If another drive fails before the rebuild finishes, you could lose data. The Rebuild Time Estimator in this calculator helps you see how long that process might take.

Q: What are RAID subgroups?

Subgroups apply to nested RAID types like RAID 50 and RAID 60 . These split your drives into smaller groups first, then stripe across those groups. For example, RAID 50 with 2 subgroups of 3 drives each creates two RAID 5 arrays striped together. Your total drive count must divide evenly into the number of subgroups.

Q: What does the file system overhead option do?

File systems like ext4 and Btrfs reserve a small percentage of your drive space for their own internal data, called metadata. This space is not available for your files. Selecting a file system in Advanced Options subtracts that overhead so you see a more realistic usable capacity number.

RAID Calculator

Updated Jun 17, 2026 By Jehan Wadia

Introduction

RAID stands for Redundant Array of Independent Disks. It is a way to combine multiple hard drives or SSDs into one storage unit. Depending on the RAID level you pick, you can get faster speeds, protection against drive failure, or both. The trade-off is that some of your total drive space is used for that protection instead of storing your files.

This free RAID calculator helps you figure out how much usable storage you will actually get from your drives. Enter the number of drives, their size, and the RAID type you want. The tool instantly shows your usable capacity, storage efficiency, fault tolerance, and estimated read and write speed gains. You can also compare two RAID levels side by side to see which one fits your needs best.

The calculator supports RAID 0, RAID 1, RAID 1E, RAID 5, RAID 5E, RAID 5EE, RAID 6, RAID 10, RAID 50, and RAID 60. It works with both uniform and mixed-capacity drive setups. Advanced options let you switch between binary and decimal units, add filesystem overhead, and estimate rebuild time after a drive failure.

How to Use Our RAID Calculator

Enter your drive details and pick a RAID type below. The calculator will show you how much usable storage you get, how much space goes to protection, and how fast your array can read and write.

Input Mode: Choose "Uniform Drives" if all your drives are the same size. Choose "Mixed Capacity" if your drives have different sizes.

Number of Drives: In uniform mode, type how many drives you plan to use in your array.

Drive Size and Unit: In uniform mode, enter the size of each drive and pick GB or TB from the dropdown.

Mixed Capacity Selection: In mixed mode, use the plus and minus buttons to set how many drives you have at each size tier.

Primary RAID Type: Pick the RAID level you want to calculate. Each option shows its name and a short description. The calculator will tell you if you need more drives for your chosen level.

Compare with a Second RAID Type: Click this button to add a second RAID level side by side. This helps you see the trade-offs between two setups at once.

Number of RAID Subgroups: This field appears only for nested RAID types like RAID 50 and RAID 60. Enter how many subgroups you want your drives split into.

Storage Unit Calculation: Found under Advanced Options. Pick "Binary" to see sizes the way your operating system reports them (GiB/TiB). Pick "Decimal" to see sizes the way drive makers label them (GB/TB).

File System Metadata Overhead: Found under Advanced Options. Choose a file system to subtract the space it reserves for its own metadata. Select "None" if you only want raw RAID numbers.

OS / SWAP Reservation: Found under Advanced Options. Check this box to set aside about 10 GB on each drive for an operating system or swap partition.

Rebuild Speed: Found under the Estimate Rebuild Time section. Enter the expected rebuild speed in MB/s or GB/hr. The calculator will estimate how long it takes to rebuild your array after a drive failure. If you are curious about general data transfer timing, our Download Time Calculator can help estimate how long large file transfers take over your network.

Calculate / Reset: Press "Calculate" to run the numbers or press "Reset" to return every field to its default value.

What Is RAID?

RAID stands for Redundant Array of Independent Disks. It is a way to combine two or more hard drives so they work together as one unit. RAID can make your storage faster, safer, or both, depending on which type you choose.

Why RAID Matters

Hard drives can fail at any time. When a drive dies, the data on it is usually gone for good. RAID helps protect against this by copying or spreading your data across multiple drives. If one drive breaks, your files can still be recovered from the remaining drives. This is called fault tolerance.

RAID can also speed things up. When data is split across several drives, your computer can read and write faster because multiple drives are doing the work at the same time. This is called striping. If you want to understand how your storage throughput fits into overall system performance, our Bandwidth Calculator can help you evaluate data transfer rates across your setup.

Common RAID Types

RAID 0 stripes data across all drives for maximum speed and full capacity, but offers zero protection. If any single drive fails, all data is lost.

RAID 1 mirrors your data by writing the same copy to every drive. It is simple and safe, but you lose half your total storage to the mirror.

RAID 5 spreads data and one parity block across at least three drives. You lose the capacity of one drive to parity, but the array survives one drive failure. It is one of the most popular choices for small servers. If you are planning a home server build, tools like our Minecraft Server RAM Calculator can help you size other hardware components alongside your storage array.

RAID 6 works like RAID 5 but uses two parity blocks instead of one. It can survive two drives failing at the same time, making it a stronger choice for larger arrays.

RAID 10 combines mirroring and striping. It needs at least four drives and uses half the total capacity for mirrors. It is fast and reliable, which makes it a top pick for databases.

The Trade-Off

No RAID level gives you everything. You always trade something. RAID 0 gives full speed and capacity but no safety. RAID 1 gives great safety but cuts your usable space in half. RAID 5 and RAID 6 balance speed, capacity, and protection, but they use some of your storage for parity data. The right choice depends on how much space you need, how fast you need it, and how important your data is. When building a system around your RAID array, use our Bottleneck Calculator to make sure your CPU, GPU, and storage are well balanced. You should also check that your power supply can handle the extra drives with a PSU Calculator, since each additional disk adds to total system power draw. Running multiple drives around the clock can also add up on your electric bill, so our Electricity Cost Calculator can help you estimate the ongoing cost.

RAID Is Not a Backup

RAID protects against drive failure, but it does not replace backups. It will not save you from accidental deletion, viruses, fire, or theft. Always keep a separate backup of any data you cannot afford to lose.

Frequently asked questions

How many drives do I need for RAID 5?

You need at least 3 drives for RAID 5. One drive's worth of space is used for parity data, so with 3 drives you get the usable capacity of 2. More drives means more usable space, but you always lose one drive's worth to parity.

What happens to my storage when I use mixed drive sizes in RAID?

Most RAID levels use the smallest drive's size for every drive in the array. If you mix a 2 TB drive with two 4 TB drives, the array treats all three as 2 TB drives. The extra space on the larger drives is wasted. The calculator shows this unused space in gray on the capacity bar.

Why does my drive show less space than the label says?

Drive makers use decimal math where 1 TB equals 1,000 GB. Your computer uses binary math where 1 TiB equals 1,024 GiB. That difference means a drive labeled 1 TB shows up as about 931 GiB in your operating system. Use the Binary option under Advanced Options to see sizes the way your OS reports them.

What does storage efficiency mean?

Storage efficiency is the percentage of your total raw drive space that you can actually use for files. For example, if you have 16 TB of raw capacity and 12 TB is usable after RAID overhead, your storage efficiency is 75%. Higher efficiency means less space lost to protection.

Which RAID level gives the most usable space?

RAID 0 gives 100% of your total drive space because it has no redundancy at all. However, if any single drive fails, you lose everything. Among RAID levels that offer protection, RAID 5 gives the most usable space because it only uses one drive's worth for parity.

What does fault tolerance mean in this calculator?

Fault tolerance is the number of drives that can break at the same time without losing your data. For example, RAID 5 can survive 1 drive failure and RAID 6 can survive 2. RAID 0 has zero fault tolerance, so any single drive failure destroys the whole array.

What are the read and write speed multipliers?

These numbers show how much faster the array is compared to a single drive. A read multiplier of 4× means the array can read roughly four times faster than one drive alone. These are theoretical maximums. Real-world speeds depend on your RAID controller, drive type, and workload.

What is a RAID rebuild and why does it matter?

A rebuild happens when a failed drive is replaced and the array reconstructs the missing data onto the new drive. During a rebuild, the array is slower and more vulnerable. If another drive fails before the rebuild finishes, you could lose data. The Rebuild Time Estimator in this calculator helps you see how long that process might take.

What are RAID subgroups?

Subgroups apply to nested RAID types like RAID 50 and RAID 60. These split your drives into smaller groups first, then stripe across those groups. For example, RAID 50 with 2 subgroups of 3 drives each creates two RAID 5 arrays striped together. Your total drive count must divide evenly into the number of subgroups.

What does the file system overhead option do?

File systems like ext4 and Btrfs reserve a small percentage of your drive space for their own internal data, called metadata. This space is not available for your files. Selecting a file system in Advanced Options subtracts that overhead so you see a more realistic usable capacity number.

Should I pick RAID 5 or RAID 6?

RAID 5 uses one drive for parity and survives one drive failure. RAID 6 uses two drives for parity and survives two failures. Pick RAID 6 if you have a large array or big drives, because rebuilds take longer and the chance of a second failure during rebuild is higher. Pick RAID 5 if you have a small array and want more usable space.

Can I use SSDs in a RAID array?

Yes. RAID works with both hard drives (HDDs) and solid-state drives (SSDs). SSDs are faster, so your array speeds will be higher. The capacity math in this calculator is the same for both drive types. Just enter your SSD size and count like you would for any drive.

What is the difference between RAID 5E and RAID 5EE?

Both include a built-in hot spare so rebuilds start right away when a drive fails. RAID 5E keeps the spare as a dedicated unused drive. RAID 5EE spreads the spare space across all drives, which gives slightly better read speed. Both use the same total capacity.

What does the compare feature do?

It lets you see two RAID levels side by side using the same set of drives. This makes it easy to compare usable space, efficiency, fault tolerance, and speed between two setups so you can choose the one that fits your needs.

Why does RAID 10 need an even number of drives?

RAID 10 creates mirrored pairs and then stripes across those pairs. Each pair needs exactly two drives. If you enter an odd number, the calculator drops one drive and shows a warning. For example, with 5 drives it will calculate RAID 10 using only 4.

What does the OS/SWAP reservation option do?

When checked, the calculator subtracts 10 GB from each drive before doing the RAID math. This accounts for space you might set aside for an operating system install or a swap partition. It gives you a more accurate picture of usable storage on drives that also run an OS.

How accurate is the rebuild time estimate?

It is a rough estimate only. Real rebuild times depend on your RAID controller, drive speed, how full the array is, system load during the rebuild, and whether any read errors happen. Use the estimate as a general guide, not an exact prediction.

What is RAID 1E and when would I use it?

RAID 1E is interspersed mirroring that works with three or more drives, including odd numbers. It spreads mirrored copies across all drives. Use it when you have an odd number of drives and want mirror-based protection. With an even count, it behaves much like RAID 10.