Raid Zfs Calculator

Estimate the usable capacity and fault tolerance of your ZFS storage pool.

Calculator

RAID Level Comparison

RAID Level	Min Disks	Fault Tolerance	Usable Capacity

Comparison of different RAID-Z levels with current settings.

What is a RAID-ZFS Calculator?

A RAID-ZFS calculator is a tool designed to help you plan and configure your ZFS (Zettabyte File System) storage pools. It allows you to estimate the total usable storage capacity you can expect from a given number of disks and a specific RAID-Z level. Beyond just capacity, this calculator also provides insights into storage efficiency and fault tolerance, which are critical for making informed decisions about your data storage strategy. This tool is invaluable for system administrators, IT professionals, and home lab enthusiasts who want to optimize their storage for performance, redundancy, or a balance of both.

The RAID-ZFS Formula and Mathematical Explanation

The calculation for usable capacity in a RAID-ZFS setup is straightforward but depends on the chosen RAID-Z level. RAID-Z works by distributing data and parity information across a set of disks.

The basic formula is:

Usable Capacity = (Number of Disks – Number of Parity Disks) * Size of Smallest Disk

The number of parity disks is determined by the RAID-Z level:

• RAID-Z1: 1 parity disk
• RAID-Z2: 2 parity disks
• RAID-Z3: 3 parity disks

Variable	Meaning	Unit	Typical Range
Number of Disks	The total count of physical disks in the VDEV (Virtual Device).	Count	3 – 20+
Disk Size	The capacity of a single disk.	TB or GB	1 TB – 22 TB
RAID-Z Level	The chosen redundancy level.	–	Z1, Z2, Z3

Practical Examples (Real-World Use Cases)

Example 1: Home Media Server

An enthusiast wants to build a home media server for storing movies, music, and photos. They have 5 disks, each with a capacity of 4 TB. They choose RAID-Z1 for a good balance of capacity and single-disk failure protection.

Inputs: 5 disks, 4 TB each, RAID-Z1

Outputs: 16 TB usable capacity, 20 TB raw capacity, fault tolerance of 1 disk.
This setup provides ample space for a large media library while protecting against a single drive failure.

Example 2: Small Business File Server

A small business needs a reliable file server for critical documents. They opt for 6 disks of 8 TB each and use RAID-Z2 for enhanced data protection, as it can withstand two simultaneous disk failures.

Inputs: 6 disks, 8 TB each, RAID-Z2

Outputs: 32 TB usable capacity, 48 TB raw capacity, fault tolerance of 2 disks.
This configuration offers robust data security, which is paramount for business-critical data.

How to Use This RAID-ZFS Calculator

Using this calculator is simple:

1. Enter the Number of Disks: Input the total number of hard drives you plan to use in your array.
2. Provide the Disk Size: Enter the capacity of a single disk in terabytes (TB). For simplicity, assume all disks are the same size.
3. Select the RAID-Z Level: Choose between RAID-Z1, RAID-Z2, and RAID-Z3 from the dropdown menu, depending on your desired level of redundancy.
4. Review the Results: The calculator will instantly display the usable capacity, raw capacity, storage efficiency, and fault tolerance.

Key Factors That Affect RAID-ZFS Results

• Number of Disks: More disks generally mean more capacity, but also more potential points of failure.
• Disk Size: Larger disks provide more raw capacity, but rebuild times after a failure can be longer.
• RAID-Z Level: This is the most critical factor. RAID-Z1 offers the most usable space but the least protection. RAID-Z3 offers the most protection but at the cost of two additional disks worth of capacity.
• VDEVs: For more complex setups, you can group disks into multiple VDEVs (Virtual Devices). This calculator focuses on a single VDEV for simplicity.
• Slop Space: ZFS reserves a small amount of space (slop space) to prevent the pool from becoming 100% full, which can degrade performance. This calculator provides a simplified estimate.
• Data Compression: ZFS supports transparent compression, which can significantly increase the effective usable space, depending on the type of data being stored.

Frequently Asked Questions (FAQ)

What is the minimum number of disks for RAID-Z?

RAID-Z1 requires a minimum of 3 disks. RAID-Z2 requires a minimum of 4 disks, and RAID-Z3 requires a minimum of 5 disks.

Can I use disks of different sizes?

Yes, but the usable capacity will be limited by the size of the smallest disk in the array. It’s generally recommended to use disks of the same size for optimal performance and capacity.

What happens if a disk fails?

If a disk fails in a RAID-Z array, the system will continue to operate in a degraded state. You can replace the failed disk, and ZFS will automatically “resilver” (rebuild) the data onto the new disk.

RAID-Z1 vs. RAID-Z2: Which is better?

RAID-Z2 provides significantly better data protection by allowing for two disk failures. For arrays with many disks or for storing critical data, RAID-Z2 is often recommended over RAID-Z1.

What is ‘slop space’?

ZFS reserves a small amount of disk space to ensure that the pool does not become completely full, which can cause performance issues. This is known as slop space.

How does ZFS prevent data corruption?

ZFS uses end-to-end checksumming to detect and correct silent data corruption. When data is read, its checksum is verified. If corruption is detected, ZFS can repair the data using the parity information or a mirrored copy.

Should I use hardware RAID with ZFS?

No, it is strongly recommended to give ZFS direct control over the disks and not use a hardware RAID controller. ZFS is designed to manage the disks itself for optimal performance and data integrity.

How much RAM do I need for ZFS?

A common rule of thumb is 1GB of RAM for every 1TB of storage, but this can vary depending on the workload. More RAM allows ZFS to cache more data, improving read performance.