---
title: "HA-NAS - Configuring the ZFS settings of a partition"
description: "Find out how to apply a usage template or custom ZFS settings (atime, recordsize, sync) to an HA-NAS partition"
url: https://docs.ovhcloud.com/en/guides/storage-and-backup/file-storage/ha-nas/nas-zfs-settings
lang: en
lastUpdated: 2026-10-29
---
> For AI agents: the complete documentation index is available at https://docs.ovhcloud.com/en/llms.txt, the full documentation bundle is available at https://docs.ovhcloud.com/en/llms-full.txt.

# HA-NAS - Configuring the ZFS settings of a partition

## Objective

Each partition of an HA-NAS service is a ZFS dataset. You can adjust three of its ZFS properties to suit the workload it stores: access time update (_atime_), maximum block size (_recordsize_) and write synchronisation (_sync_).

To make this easier, OVHcloud provides usage templates that apply a predefined combination of these settings in one step.

**This guide explains what each ZFS setting does, which values each template applies, and how to change the settings of a partition from the OVHcloud Control Panel or via the OVHcloud API.**

## Requirements

- An OVHcloud [HA-NAS service](https://www.ovhcloud.com/en-gb/storage-solutions/nas-ha/) with at least one [partition](https://docs.ovhcloud.com/en/guides/storage-and-backup/file-storage/ha-nas/nas-get-started.md)
- Access to the OVHcloud Control Panel, or to the OVHcloud API (see the [OVHcloud API first steps guide](https://docs.ovhcloud.com/en/guides/manage-and-operate/api/first-steps.md))

***

### OVHcloud Control Panel Access

- **Direct link:** "HA-NAS"
- **Navigation path:** "Bare Metal Cloud" > "HA-NAS" > Select your NAS-HA

***

## Instructions

**Warning:** The default ZFS settings suit most uses. Only change them if you know the workload stored on the partition and the impact of each setting described below.

### Understanding the ZFS settings

#### Access time update (atime)

When _atime_ is enabled, ZFS updates the last access time of a file every time it is read, so each read also generates a write.

When _atime_ is disabled (`off`), these extra writes are avoided, which improves performance for read-intensive workloads. Disable it unless an application stored on the partition relies on file access times. All the usage templates set _atime_ to `off`.

#### ZFS recordsize

The _recordsize_ is the maximum size of the blocks in which ZFS stores the data of a file. Files smaller than the _recordsize_ use a smaller block: a 16 KiB file uses a 16 KiB block (plus metadata), not a full 128 KiB block.

As a rule of thumb, align the _recordsize_ with the size of the application's reads and writes:

- **Small, random reads and writes** (databases, virtual machine disks): a small _recordsize_ avoids reading and rewriting a large block to change a few kilobytes.
- **Large, sequential reads and writes** (video files, images, backups, archives): a large _recordsize_ reduces the number of blocks and the metadata to handle, which improves throughput.

The available values are listed below. The Control Panel displays them in decimal units (1 KB = 1,000 bytes).

| Value (bytes)      | Binary size | Displayed in the Control Panel |
| ------------------ | ----------- | ------------------------------ |
| `4096`             | 4 KiB       | 4.1 KB                         |
| `8192`             | 8 KiB       | 8.2 KB                         |
| `16384`            | 16 KiB      | 16.4 KB                        |
| `32768`            | 32 KiB      | 32.8 KB                        |
| `65536`            | 64 KiB      | 65.5 KB                        |
| `131072` (default) | 128 KiB     | 131.1 KB (Default)             |
| `1048576`          | 1 MiB       | 1 MB                           |

**Note:** A new _recordsize_ only applies to files created after the change. Existing files keep the block size they were written with until they are recreated.

#### Sync

The _sync_ setting determines how ZFS handles synchronous write requests, that is, requests for which the application waits for confirmation that the data is stored on disk.

| Value                | Behaviour                                                                                                                                    | Use                                                                                                                                                                      |
| -------------------- | -------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `standard` (default) | ZFS honours synchronous write requests: the write is confirmed once the data is secured on disk. Asynchronous writes are buffered in memory. | Recommended for all uses. Combines data safety and performance.                                                                                                          |
| `always`             | Every write is handled as synchronous, even when the application does not request it.                                                        | Maximum data safety, at the cost of lower write performance.                                                                                                             |
| `disabled`           | ZFS ignores synchronous write requests and confirms them before the data is written to disk.                                                 | Very high performance, but data confirmed as written can be lost in the event of an incident. Not suitable for databases or NFS clients that rely on synchronous writes. |

**Important:** With _sync_ set to `disabled`, an application may consider data as saved when it is not yet on disk. Only use this value if you fully understand the risk of data loss.

### Usage templates

A usage template applies a predefined combination of the three settings to the partition in one step. All templates set _atime_ to `off` and _sync_ to `standard`. They only differ in the _recordsize_:

| Template                   | Intended use                                   | atime | sync       | recordsize         |
| -------------------------- | ---------------------------------------------- | ----- | ---------- | ------------------ |
| `Default`                  | General file sharing                           | `off` | `standard` | `131072` (128 KiB) |
| `Virtual machines`         | Virtual machine images                         | `off` | `standard` | `65536` (64 KiB)   |
| `Databases`                | Database storage                               | `off` | `standard` | `16384` (16 KiB)   |
| `File Systems (big files)` | Large file sharing (images, videos, streaming) | `off` | `standard` | `1048576` (1 MiB)  |

If none of these combinations suits your workload, set each value yourself with the `Custom
` option (Control Panel) or the custom parameters (API).

### Changing the ZFS settings of a partition

The change is applied to the whole partition by an asynchronous task.

#### OVHcloud Control Panel

Once your HA-NAS service is selected, open the "Partitions" tab.
In the partitions table, click the "..." button on the row of the partition concerned, then click "Configure usage (ZFS)". The **Edit settings** window opens.
**To apply a usage template:**
1. In the "Select template" drop-down list, select one of the templates: "Default", "Virtual machines", "Databases" or "File Systems (big files)".
2. Click "Edit settings" to confirm.

**To set custom values:**
1. In the "Select template" drop-down list, select "Custom". The **Access time update (atime)**, **ZFS recordsize** and **Sync** fields are displayed, filled in with the current values of the partition.
2. Adjust the values you need: the "Disable" checkbox for _atime_, a value from the "ZFS recordsize" drop-down list, and one of the "Always", "Disabled" or "Standard" options for _sync_. The default values are marked **(Default)**.
3. Click "Edit settings" to confirm.

A notification informs you once the ZFS settings of the partition have been updated.

#### OVHcloud API

All the routes below are in the _/dedicated/nasha_ section of the API console.
To retrieve the name of your service and of your partitions, use the following routes:

[GET /dedicated/nasha](https://api.eu.ovhcloud.com/console/?section=/dedicated/nasha&branch=v1#get-/dedicated/nasha)

[GET /dedicated/nasha/{serviceName}/partition](https://api.eu.ovhcloud.com/console/?section=/dedicated/nasha&branch=v1#get-/dedicated/nasha/-serviceName-/partition)

To change the ZFS settings of a partition, use the following route:

[POST /dedicated/nasha/{serviceName}/partition/{partitionName}/options](https://api.eu.ovhcloud.com/console/?section=/dedicated/nasha&branch=v1#post-/dedicated/nasha/-serviceName-/partition/-partitionName-/options)

| Parameter       | Required | Description                                                                                              |
| --------------- | -------- | -------------------------------------------------------------------------------------------------------- |
| `serviceName`   | Yes      | The internal name of your HA-NAS service                                                                 |
| `partitionName` | Yes      | Name of the partition                                                                                    |
| `templateName`  |          | Usage template to apply: `Default`, `Virtual machines`, `Databases` or `File Systems (big files)`        |
| `atime`         |          | Access time update: `off` (default) or `on`                                                              |
| `recordsize`    |          | Maximum block size, in bytes: `4096`, `8192`, `16384`, `32768`, `65536`, `131072` (default) or `1048576` |
| `sync`          |          | Write synchronisation: `standard` (default), `always` or `disabled`                                      |
To apply a template, send only the `templateName` parameter. For example, for a partition storing a database:
```json
{
  "templateName": "Databases"
}
```
To set custom values, send the `atime`, `recordsize` and `sync` parameters instead, without `templateName`:
```json
{
  "atime": "off",
  "recordsize": "65536",
  "sync": "standard"
}
```
The call returns a task. You can follow its progress with the following route:

[GET /dedicated/nasha/{serviceName}/task/{taskId}](https://api.eu.ovhcloud.com/console/?section=/dedicated/nasha&branch=v1#get-/dedicated/nasha/-serviceName-/task/-taskId-)

### Checking the ZFS settings of a partition

To check the settings applied to a partition, use the following API route:

[GET /dedicated/nasha/{serviceName}/partition/{partitionName}/options](https://api.eu.ovhcloud.com/console/?section=/dedicated/nasha&branch=v1#get-/dedicated/nasha/-serviceName-/partition/-partitionName-/options)

The response contains the current `atime`, `recordsize` and `sync` values and, in the `templateName` field, the name of the template applied to the partition, if any.

## Go further

[Getting started with a HA-NAS solution](https://docs.ovhcloud.com/en/guides/storage-and-backup/file-storage/ha-nas/nas-get-started.md)

[HA-NAS - Managing partitions via API](https://docs.ovhcloud.com/en/guides/storage-and-backup/file-storage/ha-nas/nas-partitions-api.md)

[Mounting HA-NAS via NFS share](https://docs.ovhcloud.com/en/guides/storage-and-backup/file-storage/ha-nas/nas-nfs.md)

For training or technical assistance implementing our solutions, contact your sales representative or visit our [Professional Services](https://www.ovhcloud.com/en-gb/professional-services/) page to request a quote and have your project analysed by our experts.

Join our [community of users](https://community.ovhcloud.com/).