RAID Calculator
NAS storage & upgrade planner
Free · Designed for iPad. Not verified for macOS.
Now built for iPhone Duo: results beside inputs on the open display, with the fold between them. Plus advice with one-tap fixes, and ten languages.
How much space will you actually get? RAID Calculator answers in seconds, for identical drives in classic RAID and for the mixed drives in a real NAS, whether it runs Synology, Unraid, ZFS, SnapRAID or Btrfs.
PLAN YOUR NEXT DRIVE
Real NAS boxes rarely hold identical drives. Give each bay its own size, or leave it empty, and see what your system does with them:
• Five systems: Synology SHR, SHR-2 and RAID 1, 5 or 6; Unraid; ZFS RAID-Z; SnapRAID; and Btrfs RAID1
• Every drive drawn to scale and split into what it holds: data, parity, a mirror copy, or nothing at all
• Unused capacity hatched, with the number spelled out
• Biggest Upgrade names the single purchase that unlocks the most space, with one tap to try it
• Save your current setup, then see every change compared with it (“+4 TB usable”), and Revert when you’re done
• Unraid and SnapRAID put parity on your largest drives automatically
• For ZFS, the figure ZFS itself will report, labeled as an estimate
• Advice where it matters: SnapRAID’s recommended parity count, and a note on very wide RAID-Z groups • From 2 to 12 bays for Synology, or up to 30 for Unraid, ZFS, SnapRAID and Btrfs RAID1
COMPARE SYSTEMS
See your drives under every system at once, most usable space first, with failures tolerated and unused space for each. Tap a system to switch to it and watch the same bays re-split.
CLASSIC RAID, INSTANTLY
Pick RAID 0, 1, 5, 6, 10, 50 or 60, JBOD, or ZFS RAID-Z1, Z2 or Z3, set from 1 to 24 drives and their size, and the answer is the first thing you see:
• Usable capacity, raw capacity and storage efficiency
• A drive strip showing which drives hold data, parity or mirror copies, split into groups for nested levels and RAID-Z
• How many drives can fail, honest about the cases that depend on which drives fail
• The TiB figure most NAS systems will report, and for RAID-Z what ZFS itself will report
• A rebuild-risk caution for single-parity layouts on large drives, with a one-tap switch to a safer level when your drives allow it
• Invalid setups explain themselves and offer a one-tap fix
• Relative speed and availability ratings for every level
LEARN AS YOU GO
Every RAID level and every NAS system has an info sheet: an overview, pros and cons, and typical uses, plus ratings for RAID levels. RAID-Z and every NAS system also explain how the app calculates them.
ON EVERY SCREEN
• On iPad, and on iPhone Duo opened in landscape, results sit beside inputs and systems line up side by side
• On iPad, up to 30 bays fit on screen
• On iPhone Duo, info opens in place of the inputs so the results stay in view
• Rotates to landscape on iPhone
• Built for iOS 26 with native controls and Liquid Glass
• Dark mode, Dynamic Type at every size, and full VoiceOver support that also reads each drive within a group
• English, Spanish, French, Italian, Japanese, German, Traditional Chinese, Simplified Chinese, Korean and Brazilian Portuguese
PRIVATE BY DESIGN
No account, no ads, no tracking, no network connection needed. Every calculation happens on your device.
Capacities use standard simplified formulas and don’t account for filesystem overhead, apart from the labeled ZFS estimate. Speed and availability ratings compare RAID levels with each other; they aren’t benchmarks.
Not affiliated with or endorsed by Synology Inc. Synology and SHR are trademarks of Synology Inc.
Not affiliated with or endorsed by Lime Technology, Inc. Unraid is a trademark of Lime Technology, Inc.
ZFS is a trademark of Oracle and/or its affiliates. Not affiliated with or endorsed by Oracle.
Built for iPhone Duo, with clearer advice and ten languages.
• On iPhone Duo, the closed outer display shows a single column. Opened in landscape, results sit beside inputs with the fold between them, and info opens in place of the inputs so your results stay in view
• iPhone now rotates to landscape
• The NAS comparison starts once you save your current setup, shows the setup it’s comparing against, and Revert asks first
• Advice looks different from errors and offers a one-tap fix, such as “Use RAID 6” or “Use 2 parity drives”
• RAID 50 and RAID-Z1 groups too narrow to move up now get the rebuild warning too
• VoiceOver says when a setup isn’t valid, and reads each drive within a group
• A higher-contrast accent color, darker still with Increase Contrast
• At the largest text sizes, the level and unit pickers become menus and the drive size lines up under its label
• Compare Systems opens at full height, and says when a system uses all your bays
• Now also in German, Traditional Chinese, Simplified Chinese, Korean and Brazilian Portuguese
The developer, Todd Greco, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Todd Greco
- Size
- 10.3 MB
- Category
- Utilities
- Compatibility
Requires iOS 26.0 or later.
- iPhone
Requires iOS 26.0 or later. - iPad
Requires iPadOS 26.0 or later. - Mac
Requires macOS 26.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 26.0 or later.
- iPhone
- Languages
English and 9 more
- English, French, German, Italian, Japanese, Korean, Portuguese, Simplified Chinese, Spanish, Traditional Chinese
- Age Rating
4+
- 4+
- Copyright
- © 2026