# RBD on Windows¶

The rbd command can be used to create, remove, import, export, map or unmap images exactly like it would on Linux. Make sure to check the RBD basic commands guide.

librbd.dll is also available for applications that can natively use Ceph.

Please check the installation guide to get started.

## Windows service¶

On Windows, rbd-wnbd daemons are managed by a centralized service. This allows decoupling the daemons from the Windows session from which they originate. At the same time, the service is responsible of recreating persistent mappings, usually when the host boots.

Note that only one such service may run per host.

By default, all image mappings are persistent. Non-persistent mappings can be requested using the -onon-persistent rbd flag.

Persistent mappings are recreated when the service starts, unless explicitly unmapped. The service disconnects the mappings when being stopped. This also allows adjusting the Windows service start order so that RBD images can be mapped before starting services that may depend on it, such as VMMS.

In order to be able to reconnect the images, rbd-wnbd stores mapping information in the Windows registry at the following location: SYSTEM\CurrentControlSet\Services\rbd-wnbd.

The following command can be used to configure the service. Please update the rbd-wnbd.exe path accordingly:

New-Service -Name "ceph-rbd"
-Description "Ceph RBD Mapping Service" 
-BinaryPathName "c:\ceph\rbd-wnbd.exe service"
-StartupType Automatic


Note that the Ceph MSI installer takes care of creating the ceph-rbd Windows service.

## Usage¶

### Integration¶

RBD images can be exposed to the OS and host Windows partitions or they can be attached to Hyper-V VMs in the same way as iSCSI disks.

Starting with Openstack Wallaby, the Nova Hyper-V driver can attach RBD Cinder volumes to Hyper-V VMs.

### Mapping images¶

The workflow and CLI is similar to the Linux counterpart, with a few notable differences:

• device paths cannot be requested. The disk number and path will be picked by Windows. If a device path is provided by the used when mapping an image, it will be used as an identifier, which can also be used when unmapping the image.

• the show command was added, which describes a specific mapping. This can be used for retrieving the disk path.

• the service command was added, allowing rbd-wnbd to run as a Windows service. All mappings are by default perisistent, being recreated when the service stops, unless explicitly unmapped. The service disconnects the mappings when being stopped.

• the list command also includes a status column.

The purpose of the service mode is to ensure that mappings survive reboots and that the Windows service start order can be adjusted so that RBD images can be mapped before starting services that may depend on it, such as VMMS.

The mapped images can either be consumed by the host directly or exposed to Hyper-V VMs.

### Hyper-V VM disks¶

The following sample imports an RBD image and boots a Hyper-V VM using it:

# Feel free to use any other image. This one is convenient to use for
# testing purposes because it's very small (~15MB) and the login prompt
wget http://download.cirros-cloud.net/0.5.1/cirros-0.5.1-x86_64-disk.img 
-OutFile cirros-0.5.1-x86_64-disk.img

# We'll need to make sure that the imported images are raw (so no qcow2 or vhdx).
# You may get qemu-img from https://cloudbase.it/qemu-img-windows/
# You can add the extracted location to $env:Path or update the path accordingly. qemu-img convert -O raw cirros-0.5.1-x86_64-disk.img cirros-0.5.1-x86_64-disk.raw rbd import cirros-0.5.1-x86_64-disk.raw # Let's give it a hefty 100MB size. rbd resize cirros-0.5.1-x86_64-disk.raw --size=100MB rbd device map cirros-0.5.1-x86_64-disk.raw # Let's have a look at the mappings. rbd device list Get-Disk$mappingJson = rbd-wnbd show cirros-0.5.1-x86_64-disk.raw --format=json
$mappingJson =$mappingJson | ConvertFrom-Json

$diskNumber =$mappingJson.disk_number

New-VM -VMName BootFromRBD -MemoryStartupBytes 512MB
# The disk must be turned offline before it can be passed to Hyper-V VMs
Set-Disk -Number $diskNumber -IsOffline$true
Add-VMHardDiskDrive -VMName BootFromRBD -DiskNumber $diskNumber Start-VM -VMName BootFromRBD  ### Windows partitions¶ The following sample creates an empty RBD image, attaches it to the host and initializes a partition: rbd create blank_image --size=1G rbd device map blank_image -onon-persistent$mappingJson = rbd-wnbd show blank_image --format=json
$mappingJson =$mappingJson | ConvertFrom-Json

$diskNumber =$mappingJson.disk_number

# The disk must be online before creating or accessing partitions.
Set-Disk -Number $diskNumber -IsOffline$false

# Initialize the disk, partition it and create a fileystem.
Get-Disk -Number $diskNumber |  Initialize-Disk -PassThru |  New-Partition -AssignDriveLetter -UseMaximumSize |  Format-Volume -Force -Confirm:$false


### Limitations¶

At the moment, the Microsoft Failover Cluster can’t use WNBD disks as Cluster Shared Volumes (CSVs) underlying storage. The main reason is that WNBD and rbd-wnbd` don’t support the SCSI Persistent Reservations feature yet.

## Troubleshooting¶

Please consult the Windows troubleshooting page.