Libvirt: Support for attaching volumes via SMB¶
Currently, there are Libvirt volume drivers that support network-attached file systems such as Gluster of NFS. The purpose of this blueprint is adding support for attaching volumes hosted on a SMB share.
SMB is another widely used protocol, especially in the Microsoft world. Its simplicity along with the big improvements that were introduced in SMB 3 make this type of volume backend a very good alternative.
SMB 3 brings features such as transparent failover, multichanneling using multiple NICs, encrypted communication, and RDMA. Newer versions of Samba are getting better support for the SMB 3 features, as well as supporting Active Directory membership.
Deployer will be able to attach block storage exported in the form of virtual disks on SMB shares to instances.
A new volume driver will be added in order to support attaching volumes hosted on SMB shares. The volume driver will have a similar worflow with the NFS volume driver.
The SMB volume driver will mount the SMB share on which a volume is hosted using credentials and other flags specified in the volume connection info.
This feature will be backwards compatible, supporting older versions of SMB for simple tasks. It will support using any type of SMB share, including:
from Scale-Out file servers to basic Windows shares;
Linux SMB shares using Samba;
vendor specific hardware exporting SMB shares.
Data model impact¶
REST API impact¶
The share credentials will be parsed in the volume connection info and used when mounting a SMB share.
Also, the driver will support Active Directory integration (as long as the Samba version supports it) so that it will be able to use AD credentials.
Note that as SAMBA does not support SELinux labelling, in order to be able to boot from a volume hosted on a SMB share, the virt_use_samba SELinux option will have to be enabled. This has security implications, as there will no longer be any security isolation between VM disk images.
Other end user impact¶
Other deployer impact¶
The deployer will be able to configure the path where the SMB shares will be mounted, as well as setting mount flags.
Also, the Libvirt-qemu uid and gid will have to be specified as mount flags in order to support attaching volumes because of Libvirt trying to change the owner of the volume.
In order to support SMB3 and AD integration, Samba 4.0 or later is required. Note that any version of Samba is supported by this driver but as older versions don’t support AD integration, you won’t be able to use AD based authentication. Also, in this case you must make sure that the SMB server you are trying to access has no restrictions on the SMB protocol version, being able to fall back to an older version.
Add support for mounting SMB shares.
Provide support for local shares.
This feature should be tested using one of the SMB Cinder Volume drivers already available. The existing Tempest tests along with the according unit tests should be enough for the moment in order to test this.
While a CI is being considered, for the moment Tempest tests will be run periodically for this scenario.
Using the SMB backend will be documented.
Cinder SMB Driver blueprint: https://blueprints.launchpad.net/cinder/+spec/smbfs-volume-driver