Plan your ZFS storage pool with precision. Calculate usable capacity, parity overhead, efficiency, and ARC cache recommendations for RAIDZ1, RAIDZ2, RAIDZ3, mirror, and stripe configurations.
Plan your storage architecture with confidence using these powerful features.
Supports RAIDZ1, RAIDZ2, RAIDZ3, Mirror, and Stripe configurations with accurate parity math.
Accounts for parity overhead, slop space, and provides usable storage after all reservations.
Get recommended RAM for ZFS Adaptive Replacement Cache based on your pool size.
See storage efficiency percentage and understand your pool's fault tolerance level.
Specify the number of disks, size per disk, and choose your RAID level.
Set the percentage of space reserved for ZFS internal operations (default 3%).
Click "Calculate ZFS Pool" to instantly see usable capacity, efficiency, and ARC recommendations.
Copy results to clipboard, download a report, or share with your team.
A ZFS Calculator is an essential tool for system administrators, storage engineers, and IT professionals who are planning or managing ZFS storage pools. ZFS (Zettabyte File System) is a combined file system and logical volume manager designed by Sun Microsystems that offers advanced features like pooled storage, snapshots, clones, and built-in RAID capabilities.
When designing a ZFS storage solution, one of the most critical decisions is choosing the right RAID level and understanding the trade-offs between usable capacity, performance, and fault tolerance. This ZFS storage calculator helps you answer key questions: How much usable space will I actually get? How many disks can fail without data loss? What is the storage efficiency? How much RAM should I allocate for the ARC cache?
Using this tool is straightforward. Start by entering the total number of disks you plan to use in your ZFS pool. Then specify the size of each disk — you can choose between GB, TB, or PB. Next, select your desired RAID level from the dropdown: Stripe (no redundancy), Mirror (2-way), RAIDZ1 (single parity), RAIDZ2 (double parity), or RAIDZ3 (triple parity). Finally, adjust the slop space percentage, which is the amount of space ZFS reserves for internal operations (3% is the default and generally recommended).
Once you click "Calculate ZFS Pool," the tool computes the total raw capacity, usable capacity after parity, usable capacity after slop space, storage efficiency, number of parity disks, fault tolerance level, and a recommended ARC cache size. You can then copy the results, download a report, or share the calculations with colleagues.
For example, if you have 6 disks of 10 TB each and choose RAIDZ2 (double parity), the calculator will show: Total raw capacity = 60 TB, Usable after parity = 40 TB (since 2 disks are used for parity), Usable after 3% slop space = 38.8 TB, Storage efficiency = 66.7%, Fault tolerance = up to 2 disk failures, and an ARC cache recommendation of approximately 4.85 GB. This gives you a clear picture of what to expect from your storage investment.
Whether you're building a new storage array, expanding an existing pool, or simply evaluating different RAID configurations, this ZFS calculator provides the data you need to make informed decisions. Bookmark it for quick access during your storage planning sessions.
RAIDZ1 uses single parity — one disk can fail without data loss. RAIDZ2 uses double parity — two disks can fail. RAIDZ3 uses triple parity — three disks can fail. Higher parity levels offer more fault tolerance but reduce usable storage capacity.
ZFS recommends reserving about 3% of total pool space as slop space for internal operations like transaction groups and metadata. This helps prevent the pool from running out of space and ensures smooth operation. For most use cases, 3% is sufficient.
The Adaptive Replacement Cache (ARC) is ZFS's primary read cache in RAM. It significantly improves read performance by caching frequently accessed data. A general rule of thumb is to allocate 1/8 of your usable storage as RAM for ARC, but it also depends on your workload and available system memory.
Yes, this calculator uses standard ZFS formulas and provides accurate estimates for capacity planning. However, always consult with storage experts and perform real-world testing for critical production deployments, as additional factors like ashift, compression, and deduplication can affect final usable space.
Storage efficiency is the percentage of your total raw capacity that is actually available for data storage after accounting for parity overhead. For example, RAIDZ2 with 6 disks has 66.7% efficiency because 2 out of 6 disks are used for parity.
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