Currently, there are Cinder volume drivers which make use of network-attached storage file systems such as GlusterFS of NFS. The purpose of this blueprint is adding a volume driver supporting SMB based volume backends.
SMB is a 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.
Recent versions of Samba got improved support of the SMB 3 protocol, as well as Active Directory integration.
This driver will be backwards compatible, supporting older versions of SMB. It will support using any type of SMB share, including:
- from Scale-Out file servers to basic Windows shares;
- Linux Samba shares;
- vendor specific hardware exporting SMB shares.
The proposed driver will make use of Samba in order to mount and make use of SMB shares in a secure way, supporting Active Directory based authentication.
This driver will include all the features required by the Juno release. It will have a similar flow with other netowrk attached file system drivers, managing images regarded as volumes while hosted on SMB shares.
It will include support for raw, qcow2, vhd and vhdx images. Even so, because it will use qemu-img for image related operations, it will not support yet snapshots for vhd and vhdx formats because of qemu-img’s limitations.
The snapshot management will be done in a similar way as the Gluster driver, using an additional ”.info” file containing mappings between snapshot ids and their actual paths. This is required as the path can change in time (for example when deleting a snapshot from the chain, the backing file will be changed).
Another driver based on this will be proposed for Windows environments, having full vhd/vhdx support.
The driver will periodically ensure that the chosen shares are mounted and also retrieve informations such as free space or total allocated space.
Certain volume related operations will require to be synchronized.
In order to use local shares, the share paths will be read from the Samba config file.
The user will provide a list of SMB shares on which volumes may reside. This list will be placed in a file located at a path configured in the cinder config file. This share list may contain SMB mount options such as flags or credentials.
The config file will also contain the path to the Samba config file. Oversubmit and used space ratios may also be configured.
The user will be able to choose the volume type that will be used as well as choosing whether to use sparsed or qcow2 files instead of raw files. Depending on the available qemu-img version, vhd and vhdx formats may also be used.
The volume type may be parsed as extra spec when creating a volume.
Provide support for mounting SMB shares in the remotefs client and also using local shares.
Get SMB share status such as free space or allocated space.
Provide volume related operations support using images hosted on SMB shares.
Libvirt smbfs volume driver blueprint: https://blueprints.launchpad.net/nova/+spec/libvirt-smbfs-volume-support
Hyper-V smbfs volume driver blueprint: https://blueprints.launchpad.net/nova/+spec/hyper-v-smbfs-volume-support
A Cinder CI will be testing the SMB related features.
Using the SMB backend will be documented.