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.

 

 

 

 

 

 

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.            

On June 10, 2015, sniacloud_com will be hosting a live Webcast “Hybrid Clouds Part 2: A Case Study on Building a Bridge between Public and Private Clouds.” There are significant differences in how cloud services are delivered to various categories of users. The integration of these services with traditional IT operations will remain an important success factor but also a challenge for IT managers. The key to success is to build a bridge between private and public clouds. I’ll be back to expand upon our earlier SNIA Hybrid Clouds Webcast where we looked at the choices and strategies for picking a cloud provider for public and hybrid solutions. Please join me on June 10^th to hear:

• Best practices to work with multiple public cloud providers
• The role of SDS in supporting a hybrid data fabric
• Hybrid cloud decision criteria
• Key implementation principles
• Real-world hybrid cloud use case

Please Register now and bring your questions. This will be a live and interactive event. I hope to see you there.

 

 

On June 10, 2015, sniacloud_com will be hosting a live Webcast “Hybrid Clouds Part 2: A Case Study on Building a Bridge between Public and Private Clouds.” There are significant differences in how cloud services are delivered to various categories of users. The integration of these services with traditional IT operations will remain an important success factor but also a challenge for IT managers. The key to success is to build a bridge between private and public clouds. I'll be back to expand upon our earlier SNIA Hybrid Clouds Webcast where we looked at the choices and strategies for picking a cloud provider for public and hybrid solutions. Please join me on June 10^th to hear:

• Best practices to work with multiple public cloud providers
• The role of SDS in supporting a hybrid data fabric
• Hybrid cloud decision criteria
• Key implementation principles
• Real-world hybrid cloud use case

Please Register now and bring your questions. This will be a live and interactive event. I hope to see you there.    

For the past few weeks, there has been quite a commotion on tech sites, and it was all because of a 5 year old presentation. Someone discovered a set of slides created in 2010 by then-chair of the JEDEC SSD committee, Alvin Cox of Seagate. That person misinterpreted one of the slides to mean that unpowered SSDs would retain data for only a few days in a hot room. It was reported on one site and of course picked up by several others, spreading quickly across the spectrum of sites reporting on technical matters. Finally, Alvin and a colleague gave an interview to PCWorld (www.pcworld.com/article/2925173/debunked-your-ssd-wont-lose-data-if-left-unplugged-after-all.html) setting the record straight, stating that a scenario that might cause data loss is highly unlikely, especially for consumers. Read the article for more details.

For the past few weeks, there has been quite a commotion on tech sites, and it was all because of a 5 year old presentation. Someone discovered a set of slides created in 2010 by then-chair of the JEDEC SSD committee, Alvin Cox of Seagate. That person misinterpreted one of the slides to mean that unpowered SSDs would retain data for only a few days in a hot room. It was reported on one site and of course picked up by several others, spreading quickly across the spectrum of sites reporting on technical matters. Finally, Alvin and a colleague gave an interview to PCWorld (www.pcworld.com/article/2925173/debunked-your-ssd-wont-lose-data-if-left-unplugged-after-all.html) setting the record straight, stating that a scenario that might cause data loss is highly unlikely, especially for consumers. Read the article for more details.

We received several great questions at our What’s New in NFS 4.2 Webcast. We did not have time to answer them all, so here is a complete Q&A from the live event. If you missed it, it’s now available on demand.

Q. Are there commercial Linux or windows distributions available which have adopted pNFS?

A. Yes. RedHat RHEL6.2, Suse SLES 11.3 and Ubuntu 14.10 all support the pNFS capable client. There aren’t any pNFS servers on Linux so far; but commercial systems such as NetApp (file pNFS), EMC (block pNFS), Panasas (object pNFS) and maybe others support pNFS servers. Microsoft Windows has no client or server support for pNFS.

Q. Are we able to prevent it from going back to NFS v3 if we want to ensure file lock management?

A. An NFSv4 mount (mount -t nfs4) won’t fall back to an nfs3 mount. See man mount for details.

Q. Can pNFS metadata servers forward clients to other metadata servers?

A. No, not currently.

Q. Can pNfs provide a way similar to synchronous writes? So data’s instantly safe in at least 2 locations?

A. No; that kind of replication is a feature of the data servers. It’s not covered by the NFSv4.1 or pNFS specification.

Q. Does hole punching depend on underlying file system in server?

A. If the underlying server supports it, then hole punching will be supported. The client & server do this silently; a user of the mount isn’t aware that it’s happening.

Q. How are Ethernet Trunks formed? By the OS or by the NFS client or NFS Server or other?

A. Currently, they’re not! Although trunking is specified and is optional, there are no servers that support it.

Q. How do you think vVols could impact NFS and VMware’s use of NFS?

A. VMware has committed to supporting NFSv4.1 and there is currently support in vSphere 6. vVols adds another opportunity for clients to inform the server with IO hints; it is an area of active development.

Q. In pNFS, does the callback call to the client must come from the original-called-to metadata server?

A. Yes, the callback originates from the MDS.

Q. Is hole punched in block units?

A. That depends on the server.

Q. Is there any functionality like SMB continuous availability?

A. Since it’s a function of the server, and much of the server’s capabilities are unspecified in NFSv4, the answer is – it depends. It’s a question for the vendor of your server.

Q. NFS has historically not been used in large HPC cluster environments for cluster-wide storage, for performance reasons. Do you see these changes as potentially improving this situation?

A. Yes. There’s much work being done on the performance side, and the cluster parallelism that pNFS brings will have it outperform NFSv3 once clients employ more of its capabilities.

Q. Speaking of the Amazon adoption for NFSv4.0. Do you have insight / guess on why Amazon did not select NFSv4.1, which has a lot more performance / scalability advantages over NFSv4.0?

A. No, none at all.

We received several great questions at our What's New in NFS 4.2 Webcast. We did not have time to answer them all, so here is a complete Q&A from the live event. If you missed it, it's now available on demand. Q. Are there commercial Linux or windows distributions available which have adopted pNFS? A. Yes. RedHat RHEL6.2, Suse SLES 11.3 and Ubuntu 14.10 all support the pNFS capable client. There aren't any pNFS servers on Linux so far; but commercial systems such as NetApp (file pNFS), EMC (block pNFS), Panasas (object pNFS) and maybe others support pNFS servers. Microsoft Windows has no client or server support for pNFS. Q. Are we able to prevent it from going back to NFS v3 if we want to ensure file lock management? A. An NFSv4 mount (mount -t nfs4) won't fall back to an nfs3 mount. See man mount for details. Q. Can pNFS metadata servers forward clients to other metadata servers? A. No, not currently. Q. Can pNfs provide a way similar to synchronous writes? So data's instantly safe in at least 2 locations? A. No; that kind of replication is a feature of the data servers. It's not covered by the NFSv4.1 or pNFS specification. Q. Does hole punching depend on underlying file system in server? A. If the underlying server supports it, then hole punching will be supported. The client & server do this silently; a user of the mount isn't aware that it's happening. Q. How are Ethernet Trunks formed? By the OS or by the NFS client or NFS Server or other? A. Currently, they're not! Although trunking is specified and is optional, there are no servers that support it. Q. How do you think vVols could impact NFS and VMware's use of NFS? A. VMware has committed to supporting NFSv4.1 and there is currently support in vSphere 6. vVols adds another opportunity for clients to inform the server with IO hints; it is an area of active development. Q. In pNFS, does the callback call to the client must come from the original-called-to metadata server? A. Yes, the callback originates from the MDS. Q. Is hole punched in block units? A. That depends on the server. Q. Is there any functionality like SMB continuous availability? A. Since it's a function of the server, and much of the server's capabilities are unspecified in NFSv4, the answer is – it depends. It's a question for the vendor of your server. Q. NFS has historically not been used in large HPC cluster environments for cluster-wide storage, for performance reasons. Do you see these changes as potentially improving this situation? A. Yes. There's much work being done on the performance side, and the cluster parallelism that pNFS brings will have it outperform NFSv3 once clients employ more of its capabilities. Q. Speaking of the Amazon adoption for NFSv4.0. Do you have insight / guess on why Amazon did not select NFSv4.1, which has a lot more performance / scalability advantages over NFSv4.0? A. No, none at all.

On June 3^rd 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 3^rd

On June 3^rd 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 3^rd