TrueNAS RAID Calculator

Estimate usable storage capacity for your ZFS pool configurations.

Understanding the TrueNAS RAID Calculator

A truenas raid calculator is an essential tool for anyone planning a storage array using TrueNAS, which is built upon the powerful ZFS filesystem. Unlike traditional RAID, ZFS handles storage in “pools” and “vdevs” (virtual devices), offering superior data integrity and flexibility. This calculator helps you navigate the complexities of ZFS to predict your final usable storage space based on your chosen hardware and redundancy level. Planning correctly prevents surprises and ensures your storage setup meets your needs for both space and data safety.

The Formulas Behind ZFS Capacity

The calculation for usable space in ZFS is not as simple as just subtracting parity disks. The final capacity depends on the RAID level (RAID-Z1, Z2, Z3, or Mirror), the number of disks, and their individual sizes. Here’s a simplified breakdown:

• Stripe (RAID 0): Total Capacity = (Number of Disks) × (Size per Disk)
• Mirror: Total Capacity = (Size per Disk) — Assumes a simple 2-way mirror for calculation.
• RAID-Z1 (Single Parity): Total Capacity = (Number of Disks – 1) × (Size per Disk)
• RAID-Z2 (Double Parity): Total Capacity = (Number of Disks – 2) × (Size per Disk)
• RAID-Z3 (Triple Parity): Total Capacity = (Number of Disks – 3) × (Size per Disk)

This calculator uses these formulas to provide a close estimate. For an even more detailed analysis, you might want to look into a zfs storage calculator that accounts for metadata overhead and other factors.

ZFS vdev Variable Reference

Variable	Meaning	Unit	Typical Range
Disk Count	The total number of physical drives in a single vdev.	Unitless (Integer)	3 – 12
Disk Size	The manufacturer-stated capacity of a single drive.	TB or GB	1 TB – 24 TB
Parity Disks	Number of disks reserved for data redundancy.	Unitless (Integer)	1 for RAID-Z1, 2 for RAID-Z2, 3 for RAID-Z3
Fault Tolerance	The number of drives that can fail without data loss.	Unitless (Integer)	0 to (Disk Count – 1)

Practical Examples

Example 1: Balanced Home Media Server

A user wants to build a media server with a good balance of capacity and protection. They have 5 drives of 8 TB each and choose RAID-Z2.

• Inputs: 5 Drives, 8 TB each, RAID-Z2
• Raw Capacity: 5 × 8 TB = 40 TB
• Calculation: (5 – 2) × 8 TB = 24 TB
• Result: The user gets 24 TB of usable space with the ability to withstand two drive failures. This is a robust setup for valuable media files.

Example 2: Performance-Focused Video Editing Array

A video editor needs maximum performance for 4K editing and is willing to sacrifice some redundancy. They have 4 drives of 12 TB each and choose RAID-Z1.

• Inputs: 4 Drives, 12 TB each, RAID-Z1
• Raw Capacity: 4 × 12 TB = 48 TB
• Calculation: (4 – 1) × 12 TB = 36 TB
• Result: They achieve 36 TB of usable space with single-drive fault tolerance. This provides a good blend of speed and basic protection, which might be supplemented with a separate backup solution. Considering the truenas hardware requirements is also key for performance.

How to Use This TrueNAS RAID Calculator

1. Enter Drive Count: Input the total number of physical disks you plan to use in your virtual device (vdev).
2. Set Drive Size: Enter the capacity of a single drive, then select the appropriate unit (TB or GB). The calculator handles the conversion.
3. Select RAID Level: Choose the ZFS redundancy level you want to use. The options range from no redundancy (Stripe) to high redundancy (RAID-Z3). The calculator will warn you if you don’t have enough disks for your selected level.
4. Analyze the Results: The calculator instantly displays four key metrics:
   • Usable Capacity: The primary result showing the actual storage space you’ll have.
   • Raw Capacity: The total combined size of all your disks before accounting for parity.
   • Fault Tolerance: The number of drives that can fail simultaneously without losing data.
   • Storage Efficiency: The percentage of raw capacity that is usable.
5. Visualize the Data: Use the bar chart to quickly compare your raw storage versus your usable space. A larger gap indicates higher redundancy and lower efficiency. For deeper comparisons, a raid vs mirror analysis might be helpful.

Key Factors That Affect ZFS Capacity

• RAID Level: This is the biggest factor. A mirror immediately cuts capacity by at least 50%, while RAID-Z1, Z2, and Z3 use 1, 2, or 3 disks’ worth of space for parity, respectively.
• Number of Disks: More disks increase raw capacity, but also affect efficiency. In a RAID-Z configuration, the proportional cost of parity decreases as you add more disks to a vdev.
• Vdev Structure: This calculator assumes a single vdev. Advanced users may create a pool with multiple vdevs (e.g., two 5-disk RAID-Z1 vdevs). This changes the fault tolerance and capacity calculations.
• Disk Size Consistency: ZFS pools perform best when all disks in a vdev are the same size. If you use mixed sizes, the capacity of each disk in the vdev is treated as the size of the *smallest* disk.
• Metadata Overhead: ZFS itself uses a small percentage of space for metadata, pointers, and other internal structures. This calculator provides a high-level estimate, but expect the OS to report slightly less space. This is sometimes called “slop space.”
• Data Compression: TrueNAS offers transparent compression, which can significantly increase your effective storage capacity, especially for text-based files. This calculator does not account for compression, so your real-world usable space could be higher.

Frequently Asked Questions (FAQ)

What is the best RAID level for TrueNAS?

It depends on your needs. RAID-Z2 is often recommended as a great balance between capacity, performance, and the ability to survive two disk failures. Mirrors are best for high I/O performance (like for virtual machines). If you are unsure, our raidz capacity planner can help compare options.

Why is my usable capacity less than the disk sizes combined?

This is due to data redundancy. ZFS reserves space for “parity” data, which is used to reconstruct your data if a drive fails. This overhead is what provides fault tolerance.

Can I add just one disk to my RAID-Z pool later?

No, you cannot expand a RAID-Z vdev by adding a single disk. You must add another vdev of the same or similar geometry to the pool, or replace every disk in the vdev one by one with a larger disk.

What’s the difference between TB and TiB?

Disk manufacturers market capacity in Terabytes (TB, base-10), while operating systems like TrueNAS often measure it in Tebibytes (TiB, base-2). 1 TB is approximately 0.91 TiB. This calculator uses TB for input to match drive marketing, but advanced calculators often show both.

How many disks do I need for RAID-Z2?

You need a minimum of 4 disks for RAID-Z2 (2 for data, 2 for parity). However, performance and efficiency generally improve with more disks, such as 6 to 8.

Is Stripe (RAID 0) safe to use?

Stripe offers the best performance and 100% capacity efficiency but has zero fault tolerance. If any single drive fails, all data in the pool is lost. It is not recommended for storing any important data without a robust backup plan.

Does this calculator work for TrueNAS SCALE and CORE?

Yes, the underlying ZFS capacity principles are the same for both TrueNAS CORE (based on FreeBSD) and TrueNAS SCALE (based on Linux). This truenas raid calculator is applicable to both.

What happens if I use drives of different sizes?

In a single vdev, ZFS will treat all drives as if they are the size of the smallest drive in that vdev. To avoid wasting space, always use identical drives. You can consult the truenas hardware requirements for more details.

Related Tools and Resources

Explore more of our tools and guides to build the perfect storage solution.

• ZFS Explained: A deep dive into the features and benefits of the ZFS filesystem.
• Building Your First TrueNAS Server: A step-by-step guide to hardware selection and setup.
• NAS Power Consumption Calculator: Estimate the power usage and cost of running your server.
• RAID Performance Comparison: Understand the speed differences between RAID-Z, Mirrors, and other setups.
• Storage Technology Glossary: Definitions for common terms like vdev, pool, and more.
• Contact Us: Have a question for our storage experts? Get in touch.