Block Device Mapping

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.

Prerequisites

Block storage service enabled on the platform
Available volume types configured by your administrator
Sufficient volume and storage quota

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)

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.

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).

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

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

CLI Block Device Mapping

Source credentials

source openrc.sh

openstack server create \
  --image <IMAGE_ID> \
  --boot-from-volume 50 \
  --flavor <FLAVOR> \
  --network <NETWORK> \
  my-instance

openstack server create \
  --volume <VOLUME_ID> \
  --flavor <FLAVOR> \
  --network <NETWORK> \
  my-instance

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

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

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

Your administrator configures available volume types through the deployment console. The volume types shown in the instance wizard match those configured for the platform.

Next Steps

Launch an Instance

Create an instance with the full 4-step wizard including disk configuration

Create a Volume

Pre-create volumes to attach as bootable or data disks

Volume Types

Understand available storage tiers and their characteristics

Instance Snapshots

Create snapshots of instances with their storage configuration

Core Services

Other Services

Overview

Storage Options in the Create Wizard

Boot Source and System Disk

System Disk Configuration

Data Disks

CD-ROM Device

CLI Block Device Mapping

Volume Type Selection

Next Steps

Launch an Instance

Create a Volume

Volume Types

Instance Snapshots

​Overview

​Storage Options in the Create Wizard

​Boot Source and System Disk

​System Disk Configuration

​Data Disks

​CD-ROM Device

​CLI Block Device Mapping

​Volume Type Selection

​Next Steps

Launch an Instance

Create a Volume

Volume Types

Instance Snapshots

Overview

Storage Options in the Create Wizard

Boot Source and System Disk

System Disk Configuration

Data Disks

CD-ROM Device

CLI Block Device Mapping

Volume Type Selection

Next Steps