:{#metadata
  banner="zfs_hierarchy.png"
}

# ZFS Calculators

---

A collection of calculators from around the web, for the [ZFS][] filesystem.
This was mainly done to preserve them in one place, and to experiment with
using [PyScript][] (allows python to be used for browser scripting instead of
javascript).

If you don't know much about ZFS, or need to brush up on your knowledge,
["OpenZFS: the final word in file systems"][] by Jason Rose is a fantastic
introduction.

[ZFS]: https://en.wikipedia.org/wiki/ZFS
[PyScript]: https://pyscript.net
["OpenZFS: the final word in file systems"]: https://jro.io/truenas/openzfs

\

## RAIDZ Expansion

---

The latest TrueNAS ([Electric-Eel / 24.10][]) now supports RAIDZ expansion,
which allows you to append disks to an existing vdev. This allows you to extend
you're vdevs over time, rather than having to erase the vdev, create a new one,
and restore from backup. It has one small caveat however, which is that the
existing data still uses the data-to-parity ratio and block width of the old
vdev size. This effectively means that you don't get the full capacity of your
drives until that existing data is rewritten. If you're interested in recovering
that capacity, check out [ZFS In-Place Rebalancing][] by Markus Ressel.

This calculator, based on the TrueNAS [RAIDZ extension calculator][], allows
you to determine how much space is lost compared to creating a new vdev from
scratch.

[Electric-Eel / 24.10]: https://www.truenas.com/docs/scale/24.10/gettingstarted/scalereleasenotes
[ZFS In-Place Rebalancing]: https://github.com/markusressel/zfs-inplace-rebalancing
[RAIDZ extension calculator]: https://www.truenas.com/docs/references/extensioncalculator

---

:::: side-by-side

:::

```=html
  <label style="display: block">
    <span style="display: inline-block; width: 19rem;">Drive Size (TB):</span>
    <input type="text" id="drive_size_input" style="width: 6rem;" />
  </label>

  <label style="display: block">
    <span style="display: inline-block; width: 19rem;">RAIDZ Level / Number of Parity Disks:</span>
    <select id="raidz_level_input" style="width: 6rem;">
      <option value="1">1</option>
      <option value="2">2</option>
      <option value="3">3</option>
    </select>
  </label>

  <label style="display: block">
    <span style="display: inline-block; width: 19rem;">Initial VDEV Capacity (%):</span>
  <input type="text" id="expansion_input" style="width: 6rem;" />
  </label>

  <label style="display: block">
    <span style="display: inline-block; width: 19rem;">Initial Number of Drives:</span>
  <input type="text" id="initial_input" style="width: 6rem;" />
  </label>

  <label style="display: block">
    <span style="display: inline-block; width: 19rem;">Final Number of Drives:</span>
  <input type="text" id="final_input" style="width: 6rem;" />
  </label>

  <br>

  <button mpy-click="calculate">Calculate</button>
```

:::

:::

```=html
  <b>Extend VDEV to final width all at once</b>

  <label style="display: block; padding-left: 2rem">
    <span style="display: inline-block; width: 19rem;">Capacity lost (%):</span>
    <span id="total_capacity_recovered">0%</span>
  </label>

  <label style="display: block; padding-left: 2rem">
    <span style="display: inline-block; width: 19rem;">Capacity lost (bytes):</span>
    <span id="capacity_recovered">0 TB</span>
  </label>

  <label style="display: block; padding-left: 2rem">
    <span style="display: inline-block; width: 19rem;">Capacity lost (drives):</span>
    <span id="drives_worth_recovered">0 Drives</span>
  </label>

  <b>Extend VDEV one drive at a time</b>

  <label style="display: block; padding-left: 2rem">
    <span style="display: inline-block; width: 19rem;">Capacity lost (%):</span>
    <span id="total_capacity_recovered_compound">0%</span>
  </label>

  <label style="display: block; padding-left: 2rem">
    <span style="display: inline-block; width: 19rem;">Capacity lost (bytes):</span>
    <span id="capacity_recovered_compound">0 TB</span>
  </label>

  <label style="display: block; padding-left: 2rem">
    <span style="display: inline-block; width: 19rem;">Capacity lost (drives):</span>
    <span id="drives_worth_recovered_compound">0 Drives</span>
  </label>
```

:::

::::

```=pyscript
  from pyscript import document

  def calculate(event):
      # Convert inputs
      drive_size = int(document.querySelector("#drive_size_input").value)
      raidz_level = int(document.querySelector("#raidz_level_input").value)
      expansion = float(document.querySelector("#expansion_input").value)
      initial_drives = int(document.querySelector("#initial_input").value)
      final_drives = int(document.querySelector("#final_input").value)

      # Results for installing all drives at once
      expansionPercent = expansion / 100
      percentage_decrease = (final_drives - initial_drives) / final_drives
      drives_worth_recovered = expansionPercent * raidz_level * percentage_decrease
      capacity_recovered = drive_size * drives_worth_recovered
      total_capacity_recovered = drives_worth_recovered / final_drives

      document.querySelector("#capacity_recovered").innerText = f"{capacity_recovered:.2f} TB"
      document.querySelector("#drives_worth_recovered").innerText = f"{drives_worth_recovered:.2f} Drives"
      document.querySelector("#total_capacity_recovered").innerText = f"{total_capacity_recovered:.2%}"

      # Results for installing drives one at a time
      # Calculate the sum of a finite harmonic series
      harmonic_sum = sum(1 / i for i in range(initial_drives + 1, final_drives + 1))
      drives_worth_recovered_compound = expansionPercent * raidz_level * harmonic_sum
      capacity_recovered_compound = drive_size * drives_worth_recovered_compound
      total_capacity_recovered_compound = drives_worth_recovered_compound / final_drives

      document.querySelector("#capacity_recovered_compound").innerText = f"{capacity_recovered_compound:.2f} TB"
      document.querySelector("#drives_worth_recovered_compound").innerText = f"{drives_worth_recovered_compound:.2f} Drives"
      document.querySelector("#total_capacity_recovered_compound").innerText = f"{total_capacity_recovered_compound:.2%}"
```