> For the complete documentation index, see [llms.txt](https://docs.mithril.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.mithril.ai/compute-and-storage/persistent-storage/block-storage.md).

# Block storage

{% hint style="info" %}
Block storage requires a quota to be added to your account. For access, contact your account team via Slack or email <support@mithril.ai>
{% endhint %}

Block storage gives you the most control over your storage approach by providing a blank disk that can be attached to your instances. Block storage typically requires a more lengthy setup. If you need shared storage across multiple instances, we recommend using [file share storage](/compute-and-storage/persistent-storage/file-shares.md) instead.

{% hint style="danger" %}
Block storage volumes are **single-writer**. You can only mount a volume read-write from **only one instance at a time**. Mounting the same volume read-write from multiple instances is unsupported and will likely cause filesystem and data corruption.

The only supported multi-instance pattern is mounting the volume **read-only**, with **no concurrent write mounts**. For more details, please contact support.
{% endhint %}

## Provisioning block storage

To provision block storage, go to **Storage**, select **+ Create Storage**, and select **Block**.

1. Select the region you would like to provision your Block storage in.
2. Select the size for your disk. Currently, each block storage disk has a **maximum size of 32TB.**

   NOTE: instances in us-central2-a have 15TB and instances in us-central2-b have 12.5TB of ephemeral storage.

{% hint style="info" %}
Tip: Give your disks different sizes to make it easier to find the disk you're looking for inside your VM.
{% endhint %}

## Attach storage to reservations and spot bids

Provisioned storage is available for selection while creating a reservations or spot bid. You can attach as many storage options as needed from the same region. If you select a region that does not have provisioned storage, it will not appear as an option.

For existing instances, you can attach/detach storage volumes when the instances are in a Paused state. You will need to manually mount the new volumes.

{% hint style="warning" %}
Currently, it's not possible to shrink/expand disk size.
{% endhint %}

## Using the disk from your instance

<details>

<summary>Find the disk device name(s) using lsblk</summary>

List your block devices with lsblk. Your selected disks will start from vdd and extend to however many you added in order alphabetically.

```bash
$ lsblk
```

</details>

<details>

<summary>First time only - format the disks</summary>

If this is the first time using this disk, you will need to format and define a filesystem. In the below command:

* Replace `/mount/dir/path` with the local directory where you want the disk mounted
* Replace `/dev/name` with the disk name selected from the output of `lsblk`

⚠️ Running this command will erase the disk content if previously mounted ⚠️

```bash
sudo mkdir -p /mount/dir/path
sudo mkfs.ext4 /dev/name
```

Repeat this for all disks you are formatting.

</details>

<details>

<summary>Mount the disks</summary>

Finally, mount the disk with the below, replacing `/dev/name` and `/mount/dir/path` with the local directory of where the disk will be mounted and the disk name

```bash
sudo mount -t ext4 /dev/name /mount/dir/path
sudo chown -R $USER:$USER /mount/dir/path
```

Repeat this for all disks you are mounting.

</details>

<details>

<summary>Persist mounted disks across reboots</summary>

1. Get the `UUID` of your disks

```bash
sudo blkid
```

2. Open `/etc/fstab` in your text editor

```bash
sudo vim /etc/fstab
```

3. Add the disk to your `fstab`

```bash
# Example template
UUID=DISK_UUID MOUNT_POINT ext4 OPTIONS <dump> <pass> 
```

It looks something like this. We strongly recommend using the `nofail` option to prevent instance failure in case of disk failure or disk removal.

```bash
UUID=f124a6dc-a10f-4ff4-81cd-6a3990c1aa7d /mnt/disk ext4 defaults,nofail 0 2 
```

4. Save and mount

```bash
sudo mount -a
```

</details>

## Quotas

Each project has a total storage capacity quota that accumulates usage across all regions. Contact your account team via Slack or email <support@mithril.ai> to increase your quota.


---

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