OpenStack - SNIA on Data, Networking & Storage

OpenStack Manila – A Q&A on Liberty and Mitaka

October 16, 2015October 16, 2015 Alex McDonald Leave a comment

Our recent Webcast with OpenStack Manila OpenStack Manila Project Team Lead (PTL), Ben Swartzlander, generated a lot of great questions. As promised, we’ve complied answers for all of the questions that came in. If you think of additional questions, please feel free to comment on this blog. And if you missed the live Webcast, it’s now available on-demand.

Q. Is Hitachi Data Systems contributing to the Manila project?

A. Yes, Hitachi contributed a new driver and also contributed a major new feature (migration) during Liberty. HDS was also active during the Kilo release with a different driver which is unfortunately no longer maintained.

Q. EMC has open sourced ViPER as CopperHD. Do you see any overlap between Manila/Cinder from one side and CopperHD from the other hand?

A. I’m not familiar enough with CoprHD to answer authoritatively, but I understand that there is definitely some overlap between it and Cinder, and I also expect there is some overlap with Manila. Assuming there is some overlap, I think that’s a great thing because competition within open source drives greater quality, and it’s confirmation that there is real demand for what we’re building.

Q. Could Manila be used stand-alone (without OpenStack) to create a fileshare server?

A. Yes, the only OpenStack service Manila depends on is Keystone (for authentication). Running Manila in a stand-alone fashion is a specific use case the team supports.

Q. If we are mapping the snap shot images what is the guarantee for data integrity?

A. Snapshots are typically crash-consistent copies of the filesystem at a point in time. In reality the exact guarantee depends on the backend used, and that’s something we’d like to avoid, so that the snapshot semantics are clear to the user. In the future, backends which cannot meet the crash-consistent guarantee will probably be forced to advertise a different capability so end users are aware of what they’re getting.

Q. Is there manila automation with ansible?

A. As far as I know this hasn’t been done yet.

Q. For kilo deployed in production does it work for all commercial drivers or is there a chart that says which commercial drivers support kilo?

A. The developer doc now has a table which attempts to answer this question. However, the most reliable way to see which drivers are part of the stable/kilo release would be to look at the driver directory of the code. This is an area where the docs need to improve.

Q. Could you explain consistency groups?

A. Consistency groups are a mechanism to ensure that 2 or more shares can be snapshotted in a single operation. Without CGs, you can take 2 snapshots of 2 shares but there is no guarantee that those snapshots will represent the same point in time. CGs allow you to guarantee that the snapshots are synchronized, which makes it possible to use multiple shares together for a single application and to take snapshots of that application’s data in a consistent way.

Q. How is the consistency group in Manila different from Cinder? Is it similar?

A. The designs are very similar. There are some semantic differences in terms of how you modify the membership of the CGs, but the snapshot functionality is identical.

Q. Are you considering pNFS, but I guess this will be hard since it has req. on the client as well?

A. Manila is agnostic to the data protocol so if the backend supports pNFS and Manila is asked to create an NFS share, it may very well get a share with pNFS support. Certainly Manila supports shares with multiple export locations so that on a system with multiple network interfaces, or a clustered system, Manila will tell the clients about all of the paths to the share. In the future we may want Manila to actually know the capabilities of the backends w.r.t. what version of NFS they support so that if a user requires a minimum version we can guarantee that they get that version or get a sensible error if it’s not possible.

Q. Share Replication. In what mode, Async and/or Sync?

A. We plan to support both, and the choice of which is used will be up to the administrator. Communication about which is used and any relevant information like RPO time would be out of band from Manila. The goal of the feature in Manila is to make Manila able to configure the replication relationship, and able to initiate failovers. The intention is for planned failovers to be disruptive but with no data loss, and for unplanned failovers to be disruptive, with data loss corresponding to the RPO that the administrator configured (which would be zero for synchronous replication).

Q. Can you point me to any resources with SNIA available for OpenStack? Where can I download document, videos, etc?

A. You can find several informative OpenStack on-demand Webcasts on the SNIA BrightTalk channel here.

What to Expect from OpenStack Manila Liberty

September 11, 2015September 30, 2015 Alex McDonald Leave a comment

On October 7, 2015, the SNIA Ethernet Storage Forum is pleased to present its next live Webcast on OpenStack Manila. Manila is the OpenStack file share service that provides the management of file shares (for example, NFS and CIFS) as a core service to OpenStack. Intended to be an open-standards, highly-available and fault-tolerant component of OpenStack, Manila also aims to provide API-compatibility with popular systems like Amazon EC2.

I will be moderating this Webcast, presented by the OpenStack Manila Project Team Lead (PTL), Ben Swartzlander, who will dive into:

An overview of Manila
New features that are being delivered for OpenStack Liberty (due October 2015)
A preview of Mitaka

With Liberty availability due next month, this information is extremely timely; I encourage you to register now to block your calendar. This will be a live and interactive Webcast, please bring your questions. I look forward to “seeing” you on October 7^th.

Block Storage in OpenStack Q&A

June 10, 2015June 10, 2015 Walter Boring Leave a comment

The team at SNIA-ESF and I were very pleased with how many people attended our live “Block Storage in the Open Source Cloud called OpenStack.” If you missed it, please check it out on demand. We had several great questions during the live event. As promised here are answers to all of them. If you have additional questions, please feel free to comment on this blog.

Q. How is the support for OpenStack, if we hit a roadblock or need some features?

A. The OpenStack community has many avenues for contacting developers for support. The official place to report issues, file bugs or ask for new features is Launchpad. https://launchpad.net/openstack. It is the central place for all of the many OpenStack projects to file bugs or feature requests. This is also the location where every OpenStack project tracks its current release cycle and all of the features, called blueprints. Another good source of information are the public mailing lists. A good place to start for the mailing list is here, https://wiki.openstack.org/wiki/Mailing_Lists. Finally, developers are also on the public Internet Relay Chat channels associated with their projects. The developers are live and interactive, on each of the channels. You can find the information about the IRC system that OpenStack developers use here: https://wiki.openstack.org/wiki/IRC.

Q. Why was Python chosen as the programming language? Which version of Python is used as there are incompatibilities between versions?

A. The short answer here is that Python is a great language for rapid development and deployment that is mature and has a wide variety of publicly available libraries for doing work. The current released version of OpenStack uses Python 2.7. The OpenStack community is making efforts to ensure that we can eventually migrate to Python 3.x. New libraries that are being developed have to be Python 3.x compatible.

Q. Is it possible to replicate the backed up volumes at the OpenStack layer or do you defer to the back end array for data replication?

A. Currently, there is no built in support for volume replication in Cinder. The Cinder community is actively working on how to implement volume replication in the next release Liberty, which will ship in the fall of 2015. As with any major new feature in Cinder, the community has to design the new feature core such that it works with the 40+ vendor arrays, in such a way that it’s consistent. As the array support grows, the amount of up front design becomes more and more important and difficult at the same time. We have a specification that we are currently working on that will get us closer to implementing replication.

Q. Who, or what, creates the FC zones?

A. In Cinder, the block storage project, the component that creates and manages Fibre Channel zones is called the Fibre Channel Zone manager. A good document to read up on the zone manager is here: http://www.brocade.com/downloads/documents/at_a_glance/fc-zone-manager-ag.pdf. The official OpenStack documentation on the zone manager is here: http://docs.openstack.org/kilo/config-reference/content/section_fc-zoning.html. The zone manager is automatically called after Cinder Fibre Channel volume driver exports its volume from the array. The zone manager then adds the zones as requested by the driver to make the volume available to the virtual machine.

Q. Does the Cinder and Nova attachment process work over VLANs?

A. Yes. It’s entirely dependent on how the OpenStack admin deploys the Nova and Cinder services. As long as the Nova hosts can see the Cinder services and arrays behind the Cinder volume drivers, then it should just work.

Q. Is the FCZM a native component of the Cinder project? Or is it an add-on?

A. As I mentioned earlier, the Fibre Channel zone manager is part of the Cinder project. There has been some discussions, as part of the Cinder community, to possibly break out the zone manager into it’s own Python library, in which case it would be available to any Python project. Currently, it’s built into Cinder itself.

Q. Does Cinder involve itself in the I/O path as well or is it only the control path responsible for allocating storage?

A. Cinder is almost entirely control plane provisioning mechanism only. There are a few operations where the Cinder services actually does I/O. When a user wants to create an image from a volume, then Cinder attaches the volume to itself, and then copies the bytes from the volume into an image. Cinder also has a backup service that allows a user to backup a volume to an external service. In that case, the Cinder backup service directs copying the bytes into the configured backup storage. When Cinder attaches a volume to a Nova VM, or a bare metal node, Cinder is not involved in any I/O. Cinder’s job is to simply ensure that the volume is exported from the back-end array and make it available to Nova to see. After that, it’s entirely up to the transport protocol, iSCSI, FC, NFS, etc. to do the I/O for the volume.

Q. Is Nova aware of the LUN usage %?

A. Nova doesn’t track statistics against the volumes that it has attached to its virtual machines.

Q. Where do the vendor specific parts of Cinder fit in? Are there vendor specific “volume managers”?

A. The vendor specific components of Cinder exist in what are called Cinder volume drivers. Those drivers are really nothing more than a python module that conforms to a volume driver API that is defined by the Cinder volume manager. You can get an idea of what the features that the drivers can support on the Cinder Support Matrix here:

https://wiki.openstack.org/wiki/CinderSupportMatrix

Q. If Cinder is only for control plane, which project in OpenStack is for data path?

A. There isn’t a project in OpenStack that manages the data path for volumes.

Q. Is there a volume detachment process as well and when does that come into play?

A. My presentation primarily focused around one aspect of the interaction between Nova and Cinder, which was volume attachment. I briefly discussed the volume detachment process, but it is conducted in basically the same way. An end user asks Nova to detach the volume. Nova then removes the volume from the VM, then removes the SCSI device from the compute host itself, and then tells Cinder to terminate the connection from the array to the compute host.

Q. If a virtual machine is moved to a different physical machine, how’s that handled in Cinder?

A. This process in OpenStack is called live migration. Nova does all of the work of moving the VM’s data, from one host to another. One facet of that is migrating any Cinder volume that may be attached to the VM. Nova understands which volumes are attached to the VM and knows which one of those volume(s) are Cinder volumes. When the VM is migrated, Nova coordinates with Cinder to ensure that all volumes are attached to the destination host and VM, as well as ensures that the volumes are detached from the originating compute host.

Q. Why doesn’t Cinder use SNIA SMI-S API to manage/consume SAN, NAS or Switch fabric instead of each storage vendor building Cinder drivers? SMI already covers all scenarios for the Cinder scenarios for FC, iSCSI, SAS etc.

A. Cinder itself doesn’t really manage the storage array communication itself. It’s entirely up to the individual vendor drivers to decide how best to communicate with its storage array. The HP 3PAR volume driver uses REST to communicate with the array, as do several other vendor drivers in Cinder. Other drivers use ssh. There are no strict rules on how a Cinder volume driver can choose to communicate with its back-end. This allows vendors to make the best use of their array interfaces as they see fit.

Q. Are there Horizon extensions or extension points for showing what physical resources your storage is coming from? Or is that something a storage vendor would need to implement?

A. Horizon doesn’t really know much about where storage is coming from other than it’s a Cinder volume. Horizon uses the available Cinder APIs to talk to Cinder to do work and fetch information about Cinder’s resources. I know of a few vendors that are writing Horizon plugins that add extra capabilities to view more detailed information about their specific array. As of today though, there is no API in Cinder to describe the internals of a volume on the vendor’s array.