> ## Documentation Index
> Fetch the complete documentation index at: https://docs.xloud.tech/llms.txt
> Use this file to discover all available pages before exploring further.

# Block Device Mapping

> Control how storage volumes are presented to Xloud Compute instances at launch. Configure boot-from-volume, system disks, data disks, and CD-ROM devices.

## Overview

Block device mapping controls how storage is attached to an instance at launch time.
The Dashboard's Instance Create wizard provides a visual interface for configuring
the system disk, additional data disks, and CD-ROM devices. Understanding these
options helps you choose the right storage configuration for your workloads.

<Note>
  **Prerequisites**

  * Block storage service enabled on the platform
  * Available volume types configured by your administrator
  * Sufficient volume and storage quota
</Note>

***

## Storage Options in the Create Wizard

The **Step 1 (Base Config)** of the Instance Create wizard provides these storage
configuration options:

### Boot Source and System Disk

| Source                | Boot From Volume | Result                                                           |
| --------------------- | ---------------- | ---------------------------------------------------------------- |
| **Image**             | Yes (default)    | Creates a new persistent system disk from the image              |
| **Image**             | No               | Boots directly from image (ephemeral root disk — lost on delete) |
| **Instance Snapshot** | Automatic        | System disk configuration inherited from snapshot                |
| **Bootable Volume**   | N/A              | Boots from existing volume (count limited to 1)                  |

<Warning>
  Instances booted without a persistent volume (**Boot From Volume = No**) lose
  their root disk when deleted. Always use boot-from-volume for production workloads
  that need data persistence.
</Warning>

### System Disk Configuration

When **Boot From Volume** is set to Yes, configure the system disk:

| Field                     | Description                                                                     |
| ------------------------- | ------------------------------------------------------------------------------- |
| **Volume Type**           | Select from available storage backends (e.g., SSD, HDD tiers)                   |
| **Size (GiB)**            | Minimum is the largest of: flavor disk size, image minimum disk, and image size |
| **Delete on Termination** | Whether to delete the boot volume when the instance is deleted                  |

### Data Disks

Click **Add Data Disks** to attach additional persistent volumes at launch. Each
data disk has the same configuration options as the system disk (Volume Type, Size,
Delete on Termination).

<Tip>
  Limit the number of attached disks to 16 or fewer for optimal I/O performance.
  The dashboard shows a recommendation when adding data disks.
</Tip>

### CD-ROM Device

The wizard supports attaching a CD-ROM device at launch time:

| CD-ROM Source | Description                                          |
| ------------- | ---------------------------------------------------- |
| **None**      | No CD-ROM attached (default)                         |
| **Image**     | Mount an image (e.g., ISO) as a virtual CD-ROM drive |
| **Volume**    | Mount an existing volume as a CD-ROM drive           |

<Info>
  **Xloud-Developed** — The CD-ROM attachment feature in the instance create wizard
  is developed by Xloud and ships with XAVS / XPCI.
</Info>

***

## CLI Block Device Mapping

<Tabs>
  <Tab title="CLI" icon="terminal">
    ```bash title="Source credentials" theme={null}
    source openrc.sh
    ```

    <CodeGroup>
      ```bash title="Boot from image with persistent volume" theme={null}
      openstack server create \
        --image <IMAGE_ID> \
        --boot-from-volume 50 \
        --flavor <FLAVOR> \
        --network <NETWORK> \
        my-instance
      ```

      ```bash title="Boot from existing volume" theme={null}
      openstack server create \
        --volume <VOLUME_ID> \
        --flavor <FLAVOR> \
        --network <NETWORK> \
        my-instance
      ```

      ```bash title="Advanced block device mapping" theme={null}
      openstack server create \
        --block-device source=image,id=<IMAGE_ID>,dest=volume,size=50,bootindex=0,shutdown=remove \
        --block-device source=blank,dest=volume,size=100,shutdown=preserve \
        --flavor <FLAVOR> \
        --network <NETWORK> \
        my-instance
      ```
    </CodeGroup>

    **Block device mapping parameters**:

    | Parameter   | Values                                 | Description                                             |
    | ----------- | -------------------------------------- | ------------------------------------------------------- |
    | `source`    | `image`, `volume`, `snapshot`, `blank` | Source type for the block device                        |
    | `dest`      | `volume`, `local`                      | Destination — persistent volume or ephemeral local disk |
    | `id`        | UUID                                   | Source resource ID (for image, volume, or snapshot)     |
    | `size`      | Integer (GiB)                          | Volume size                                             |
    | `bootindex` | `0` = boot, `-1` = non-boot            | Boot order (`0` for system disk)                        |
    | `shutdown`  | `remove`, `preserve`                   | Delete behavior on instance termination                 |
  </Tab>
</Tabs>

***

## Volume Type Selection

When creating system or data disks, the available volume types depend on your
platform's storage backend configuration. Common tiers include:

| Tier        | Typical Backend             | Use Case                         |
| ----------- | --------------------------- | -------------------------------- |
| **SSD**     | Ceph SSD pool or local NVMe | Databases, high-IOPS workloads   |
| **HDD**     | Ceph HDD pool or NFS        | Archival, log storage, bulk data |
| **Default** | Platform default tier       | General-purpose workloads        |

<Note>
  Your administrator configures available volume types through
  [XDeploy](/deployment). The volume types shown in the instance wizard
  match those configured for the platform.
</Note>

***

## Next Steps

<CardGroup cols={2}>
  <Card title="Launch an Instance" href="/services/compute/launch-instance" color="#197560">
    Create an instance with the full 4-step wizard including disk configuration
  </Card>

  <Card title="Create a Volume" href="/services/storage/create-volume" color="#197560">
    Pre-create volumes to attach as bootable or data disks
  </Card>

  <Card title="Volume Types" href="/services/storage/volume-types" color="#197560">
    Understand available storage tiers and their characteristics
  </Card>

  <Card title="Instance Snapshots" href="/services/compute/snapshots" color="#197560">
    Create snapshots of instances with their storage configuration
  </Card>
</CardGroup>