Native Rest Block Driver

https://blueprints.launchpad.net/cinder/+spec/restblock-driver

We, at scality, are working on a Linux native kernel driver: Rest Block Driver. (it is on github, but still private as we want to reach a certain point before releasing it). This is a kernel driver that is able to talk to a REST-based storage service (we plan to eventually support multiple rest backends), in order to attach the files from that storage as native block devices on the host linux. One of the key points is that it allows a REST-based volume storage to take advantage of linux’s block driver cache.

Problem description

As a company, we are interested in providing an Openstack integration to our clients, and as such, we want to provide a new driver for cinder to drive and make use of the aforementionned Rest Block Driver.

This block driver currently offers the following simple features:

  • Mirror-server list management (failover and load balancing)
  • Provisionning (create/extend/delete)
  • Automatic attach/detach of volumes (practical for use within cinder)

Also, we have plans for a few features that should come shortly:

  • Storage Pool management to provide volumes from different storage pools. Each pool will have their own list of mirrors to choose from.
  • Real failover implementation
  • Multiple back-ends support (for multiple REST-like protocols implementations, ours being a CDMI implementation)
  • Native snapshot management

Use Cases

Proposed change

The Rest Block Driver is mostly controlled through the /sys file system. Thus, most of the control operations will be implemented using the process utils module. For the general feature implementation, here is how we plan to support the multiple required features of a Cinder driver:

  • Provisionning (create/extend/delete) : natively supported by the kernel driver
  • Automatic attach of volumes at setup-time: Natively supported by the kernel driver
  • Snapshots (create/delete) : Supported through LVM tool classes/functions
  • Copy To/From Image: Supported thanks to image_utils
  • Volume Cloning (from volume or from snapshot): Supported through copy utils

Please not that this reflects the current state of the kernel driver, and might evolve.

In the future it will provide a way to manage the snapshots from the driver itself, but it is not yet supported. Thus, the driver will use the lvm code tools to manage thin snapshot provisionning and support snapshots for the volumes exposed by our Rest Block Driver.

Alternatives

None

Data model impact

None

REST API impact

None

Security impact

Since this driver is controlled through the /sys file system, it requires administrative privileges to be controlled (ie. to write/read from /sys files).

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

As this is a 3rd-party provided driver, it implies setting up the said software first. Other than that, only the new driver-specific configuration values will be added.

Developer impact

None

Implementation

Assignee(s)

Primary assignee:
<dav.pineau@gmail.com>
Other contributors:
None

Work Items

Provide a cinder driver leveraging both LVM for non-implemented features and the driver itself for the natively supported features.

Dependencies

None

Testing

The driver does not bring any modification to the existing APIs and behaviors. As such, no new tempest tests should be required in our understanding.

As this driver relies on a vendor-specific software, the gate obviously cannot test the driver. We are currently setting up third-party CI testing for both our previous driver (Scality Sofs) and this new one.

Documentation Impact

None

References

None