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    Q&A – OpenStack Mitaka and Data Protection

    July 19th, 2016

    At our recent SNIA Webcast “Data Protection and OpenStack Mitaka,” Ben Swartzlander, Project Team Lead OpenStack Manila (NetApp), and Dr. Sam Fineberg, Distinguished Technologist (HPE), provided terrific insight into data protection capabilities surrounding OpenStack. If you missed the Webcast, I encourage you to watch it on-demand at your convenience. We did not have time to get to all of out attendees’ questions during the live event, so as promised, here are answers to the questions we received.

    Q. Why are there NFS drivers for Cinder?

     A. It’s fairly common in the virtualization world to store virtual disks as files in filesystems. NFS is widely used to connect hypervisors to storage arrays for the purpose of storing virtual disks, which is Cinder’s main purpose.

     Q. What does “crash-consistent” mean?

     A. It means that data on disk is what would be there is the system “crashed” at that point in time. In other words, the data reflects the order of the writes, and if any writes are lost, they are the most recent writes. To avoid losing data with a crash consistent snapshot, one must force all recently written data and metadata to be flushed to disk prior to snapshotting, and prevent further changes during the snapshot operation.

    Q. How do you recover from a Cinder replication failover?

     A. The system will continue to function after the failover, however, there is currently no mechanism to “fail-back” or “re-replicate” the volumes. This function is currently in development, and the OpenStack community will have a solution in a future release.

     Q. What is a Cinder volume type?

     A. Volume types are administrator-defined “menu choices” that users can select when creating new volumes. They contain hidden metadata, in the cinder.conf file, which Cinder uses to decide where to place them at creation time, and which drivers to use to configure them when created.

     Q. Can you replicate when multiple Cinder backends are in use?

     A. Yes

     Q. What makes a Cinder “backup” different from a Cinder “snapshot”?

     A. Snapshots are used for preserving the state of a volume from changes, allowing recovery from software or user errors, and also allowing a volume to remain stable long enough for it to be backed up. Snapshots are also very efficient to create, since many devices can create them without copying any data. However, snapshots are local to the primary data and typically have no additional protection from hardware failures. In other words, the snapshot is stored on the same storage devices and typically shares disk blocks with the original volume.

    Backups are stored in a neutral format which can be restored anywhere and typically on separate (possibly remote) hardware, making them ideal for recovery from hardware failures.

     Q. Can you explain what “share types” are and how they work?

     A. They are Manila’s version of Cinder’s volume types. One key difference is that some of the metadata about them is not hidden and visible to end users. Certain APIs work with shares of types that have specific capabilities.

     Q. What’s the difference between Cinder’s multi-attached and Manila’s shared file system?

    A. Multi-attached Cinder volumes require cluster-aware filesystems or similar technology to be used on top of them. Ordinary file systems cannot handle multi-attachment and will corrupt data quickly if attached more than one system. Therefore cinder’s multi-attach mechanism is only intended for fiesystems or database software that is specifically designed to use it.

    Manilla’s shared filesystems use industry standard network protocols, like NFS and SMB, to provide filesystems to arbitrary numbers of clients where shared access is a fundamental part of the design.

     Q. Is it true that failover is automatic?

     A. No. Failover is not automatic, for Cinder or Manila

     Q. Follow-up on failure, my question was for the array-loss scenario described in the Block discussion. Once the admin decides the array has failed, does it need to perform failover on a “VM-by-VM basis’? How does the VM know to re-attach to another Fabric, etc.?

    A. Failover is all at once, but VMs do need to be reattached one at a time.

     Q. What about Cinder? Is unified object storage on SHV server the future of storage?

     A. This is a matter of opinion. We can’t give an unbiased response.

     Q. What about a “global file share/file system view” of a lot of Manila “file shares” (i.e. a scalable global name space…)

     A. Shares have disjoint namespaces intentionally. This allows Manila to provide a simple interface which works with lots of implementations. A single large namespace could be more valuable but would preclude many implementations.



    Block Storage in OpenStack Q&A

    June 10th, 2015

    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:


    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.







    New Webcast: Block Storage in the Open Source Cloud called OpenStack

    May 26th, 2015

    On June 3rd at 10:00 a.m. SNIA-ESF will present its next live Webcast “Block Storage in the Open Source Cloud called OpenStack.” Storage is a major component of any cloud computing platform. OpenStack is one of largest and most widely supported Open Source cloud computing platforms that exist in the market today. The OpenStack block storage service (Cinder) provides persistent block storage resources that OpenStack Nova compute instances can consume.

    I will be moderating this Webcast, presented by a core member of the OpenStack Cinder team, Walt Boring. Join us, as we’ll dive into:

    • Relevant components of OpenStack Cinder
    • How block storage is managed by OpenStack
    • What storage protocols are currently supported
    • How it all works together with compute instances

    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 June 3rd

    OpenStack Cloud Storage Q&A

    January 21st, 2015

    More than 300 people have seen our Webcast “OpenStack Cloud Storage.” If you missed it, it’s now available on demand. It was a great session with a lot of questions from attendees. We did not have time to address them all – so here is a complete Q&A. If you think of any others, please comment on this blog. Also, mark your calendar for January 29th when the SNIA Cloud Storage Initiative will continue its Developers Tutorial Series with a live Webcast on OpenStack Manila.

    Q. Is it correct to say that one can use OpenStack on any vendor’s hardware?

    A. Servers, yes, assuming the hardware is supported by Linux. Block storage requires a driver, and not all vendor systems have Cinder drivers.

    Q. Is there any OpenStack investigation and/or development in the storage networking area?

    A. Cinder includes support for FC and iSCSI. As of Icehouse, the FC support also includes auto-zoning. 

    Q. Is there any monetization going on around OpenStack, like we see for distros of Linux?

    A. Yes, there are already several commercial distributions available.

    Q. Is erasure code needed to get a positive business case for Swift, when compared with traditional storage systems?

    A. It is a way to reduce the cost of replication. Traditional storage systems typically already have erasure coding, in the form of RAID. Systems without erasure coding end up using more storage to achieve the same level of protection due to their use of 3-way replication.

    Q. Is erasure code currently implemented in the current Swift release?

    A. No, it is a separate development stream, which has not been merged yet.

    Q. Any limitation on the number of objects per container or total number of objects per Swift cluster?

    A. Technically there are no limits. However, in practice, the fact that the containers are implemented using SQL lite limits their size to a million or maybe a few million objects per container. However, due to the way that Swift partitions its metadata, each user can also have millions of containers, and there can be millions of users. So practically speaking, the total system can support an unlimited number of objects.

    Q. What are some of the technical reasons for an enterprise to select Swift vs. Amazon S3? In other words, are they pretty much direct alternatives, or does each have its own preferred use cases?

    A. They are more or less direct alternatives. There are some minor differences, but they are made for the same purpose. That said, S3 is only available from Amazon. There are some S3 compatible systems, but most of those also support Swift. Swift, on the other hand, is available open source or from multiple vendors. So if you want to run it in your own data center, or in a public cloud other than Amazon, you probably want Swift.

    Q. If I wanted to play around with Open Stack, Cinder, and Swift in a lab environment (or in my basement), what do I need and how do I get started?

    A. openstack.org is the best place to start. The “devstack” distribution is also good for playing around.

    Q. Will you be showing any features for Kilo?

    A. The “Futures” I showed will likely be Kilo features, though the final decision of what will be in Kilo won’t happen until just before release.

     Q. Are there any plans to implement data encryption in Cinder?

    A. I believe some of the back ends can support encryption already. Cinder is really just a provisioning and orchestration layer. Encryption is a data path feature, so it would need to be implemented in the back end.

    Q. Some time back I heard OpenStack Swift is going to come up with block storage as well, any timeline for that?

    A. I haven’t heard this, Swift is object storage.

    Q. The performance characteristics of Cinder block services can vary quite widely. Is there any standard measure proposed within OpenStack to inform Nova or the application about the underlying Cinder block performance characteristics?

    A. Volume types were designed to enable clouds to provide different levels of service. The meaning of these types is up to the cloud administrator. That said, Cinder does expose QoS features like minimum/maximum IOPS.

    Q. Is the hypervisor talking to a cinder volume or to (for example) a NetApp or EMC volume?

    A. The hypervisor talks to a volume the same way it does outside of OpenStack. For example, the KVM hypervisor can talk to volumes through LVM, or can mount SAN volumes directly.

    Q. Which of these projects are most production-ready?

    A. This is a hard question, and depends on your definition of production ready. It’s hard to do much without Nova, Glance, and Horizon. Most people use Cinder too, and Swift has been in production at HP and Rackspace for years. Neutron has a lot of complexity, so some people still use Nova network, but that has many limitations. For toy clouds you can avoid using Keystone, but you need it for a “production” cluster. The best way to get a “production ready” OpenStack is to get a supported commercial distribution.

    Q. Are there any Plugfests?

    A. No, however, the Cinder team has a fairly extensive and continuous integration process that drivers need to pass through. Swift does not because it doesn’t officially “support” any plugins.




    OpenStack Cloud Storage Webcast Preview

    December 22nd, 2014

    On January 14, 2015, the CSI continues its Developer Tutorial series by hosting a live Webcast on OpenStack Cloud Storage. As you likely know, OpenStack is an open source cloud operating system that provides pools of compute, storage, and networking.

    OpenStack is currently being developed by thousands of developers from hundreds of companies across the globe, and is the basis of multiple public and private cloud offerings.  Register now for this SNIA-CSI Webcast to hear Sam Fineberg, Distinguished Technologist at HP discuss:

    • Storage aspects of OpenStack including the core projects for block storage (Cinder) and object storage (Swift)
    • Emerging shared file service
    • Common configurations and use cases for these technologies
    • Interaction with the other parts of OpenStack
    • New developments in Cinder and Swift that enable advanced array features, QoS, new storage fabrics, and new types of drives.

    I’ll be moderating this live event and Sam and I will be available to answer your specific questions. It should be an informative and interactive session. I hope you’ll join us!