Get your download engines running, vSphere 6.0 is here!

Yes the day is finally there, vSphere 6.0 / SRM / VSAN (and more) finally available. So where do you find it? Well that is simple… here:

Have fun!

All Flash VSAN – One versus multiple disk groups

A while ago I wrote this article on the topic of “one versus multiple disk groups“. The summary was that you can start with a single disk group, but that from a failure domain perspective having multiple disk groups is definitely preferred. Also from a performance stance there could be a benefit.

So the question now is, what about all-flash VSAN? First of all, same rules apply: 5 disk groups max, each disk group 1 SDD for caching and 7 devices for capacity. There is something extra to consider though. It isn’t something I was aware off until I read the excellent Design and Sizing Guide by Cormac. It states the following:

In version 6.0 of Virtual SAN, if the flash device used for the caching layer in all-flash configurations is less than 600GB, then 100% of the flash device is used for cache. However, if the flash cache device is larger than 600GB, the only 600GB of the device is used for caching. This is a per-disk group basis.

Now for the majority of environments this won’t really be an issue as they typically don’t hit the above limit, but it is good to know when doing your design/sizing exercise. The recommendation of 10% cache to capacity ratio still stands, and this is used capacity before FTT. If you have a requirement for a total of 100TB, then with FTT=1 that is roughly 50TB of usable capacity. When it comes to flash this means you will need a total of max 5TB flash. That is 5TB of flash in total, with 10 hosts that would be 500GB per host and that is below the limit. But with 5 hosts that would be 1TB per host which is above the 600GB mark and would result in 400GB per host being unused.

When there is a requirement to have more than 600GB of write cache capacity for all-flash it is required to create multiple disk groups. Personally I would always recommend this anyway. So when you do the sizing make sure to take this in to consideration and create multiple diskgroups when you have the chance!

Virtual Volumes primer

I was digging through my blog for a link to a virtual volumes primer article and I realized I never wrote one. I did an article which described what Virtual Volumes (VVol) is in 2012 but that is it. I am certain that Virtual Volumes is a feature that will be heavily used with vSphere 6.0 and beyond, so it was time to write a primer. What is Virtual Volumes about? What will they bring to the table?

First and foremost, Virtual Volumes was developed to make your life (vSphere admin) and that of the storage administrator easier. This is done by providing a framework that enables the vSphere administrator to assign policies to virtual machines or virtual disks. In these policies capabilities of the storage array can be defined. These capabilities can be things like snapshotting, deduplication, raid-level, thin / thick provisioning etc. What is offered to the vSphere administrator is up to the Storage administrator, and of course up to what the storage system can offer to begin with. When a virtual machine is deployed and a policy is assigned then the storage system will enable certain functionality of the array based on what was specified in the policy. So no longer a need to assign capabilities to a LUN which holds many VMs, but rather a per VM or even per VMDK level control. So how does this work? Well lets take a look at an architectural diagram first.

Virtual Volumes primer

The diagram shows a couple of components which are important in the VVol architecture. Lets list them out:

  • Protocol Endpoints aka PE
  • Virtual Datastore and a Storage Container
  • Vendor Provider / VASA
  • Policies
  • Virtual Volumes

Lets take a look at all of these three in the above order. Protocol Endpoints, what are they?

Protocol Endpoints are literally the access point to your storage system. All IO to virtual volumes is proxied through a Protocol Endpoint and you can have 1 or more of these per storage system, if your storage system supports having multiple of course. (Implementations of different vendors will vary.) PEs are compatible with different protocols (FC, FCoE, iSCSI, NFS) and if you ask me that whole discussion with Virtual Volumes will come to an end. You could see a Protocol Endpoint as a “mount point” or a device, and yes they will count towards your maximum number of devices per host (256). (Virtual Volumes it self won’t count towards that!)

Next up is the Storage Container. This is the place where you store your virtual machines, or better said where your virtual volumes end up. The Storage Container is a storage system logical construct and is represented within vSphere as a “virtual datastore”. You need 1 per storage system, but you can have many when desired. To this Storage Container you can apply capabilities. So if you like your virtual volumes to be able to use array based snapshots then the storage administrator will need to assign that capability to the storage container. Note that a storage administrator can grow a storage container without even informing you. A storage container isn’t formatted with VMFS or anything like that, so you don’t need to increase the volume in order to use the space.

But how does vSphere know which container is capable of doing what? In order to discover a storage container and its capabilities we need to be able to talk to the storage system first. This is done through the vSphere APIs for Storage Awareness. You simply point vSphere to the Vendor Provider and the vendor provider will report to vSphere what’s available, this includes both the storage containers as well as the capabilities they possess. Note that a single Vendor Provider can be managing multiple storage systems which in its turn can have multiple storage containers with many capabilities. These vendor providers can also come in different flavours, for some storage systems it is part of their software but for others it will come as a virtual appliance that sits on top of vSphere.

Now that vSphere knows which systems there are, what containers are available with which capabilities you can start creating policies. These policies can be a combination of capabilities and will ultimately be assigned to virtual machines or virtual disks even. You can imagine that in some cases you would like Quality of Service enabled to ensure performance for a VM while in other cases it isn’t as relevant but you need to have a snapshot every hour. All of this is enabled through these policies. No longer will you be maintaining that spreadsheet with all your LUNs and which data service were enabled and what not, no you simply assign a policy. (Yes, a proper naming scheme will be helpful when defining policies.) When requirements change for a VM you don’t move the VM around, no you change the policy and the storage system will do what is required in order to make the VM (and its disks) compliant again with the policy. Not the VM really, but the Virtual Volumes.

The great thing about Virtual Volumes is the fact that you know have a granular control over your workloads. Some storage systems will even allow you to assign IO profiles to your VM to ensure optimal performance. Also, when you delete a VM the virtual volumes will be deleted and the space will automatically be reclaimed by the storage system, no more fiddling with vmkfstools. Another great thing about virtual volumes is that even when you delete something within your VM this space can also be reclaimed by the storage system. When your storage system supports T10 UNMAP that is.

That is in short how Virtual Volumes work and what they bring. You as the vSphere administrator create policies and assign those to VMs, while the storage administrator manages capacity and capabilities. Easy right?!

Virtual Volumes and queueing

I was reading an article last week by Ray Lucchesi on Virtual Volumes and queueing. In that article (and podcast) Ray (and friends on the podcast) describe Virtual Volumes and the benefits they bring but also a potential danger. I have written about Virtual Volumes before and if you don’t know what it is or does then I recommend reading those articles. I have been wondering as well, how all of this works, as I also felt that there could easily be a bottleneck. I had some conversations over the last couple of weeks and I figured I would share it with you instead of just leaving a comment on Ray’s blog. Lets look at an architectural diagram first:

In the diagram above (which I borrowed from the vSphere Storage blog, thanks Rolo) you see two important constructs which are part of the overall VVOL architecture namely the Storage Container aka Virtual Datastore and the Protocol Endpoint (PE). The Storage Container is where the VVOLs will be stored. The IO though is proxied through the Protocol Endpoint. You can imagine that if we would not do this and expose every single VVOL directly to vSphere that you would have 1000s of devices connected to vSphere, and as you know vSphere has a 256 device limit at the moment. This would never scale, and as such the Protocol Endpoint is used as an access point to a VVOL capable storage system.

Now think about a VMFS volume and look at the VVOL architectural diagram again. Yes, there is a potential bottleneck indeed. However, what the diagram does not show is that you can have multiple Protocol Endpoints. Ray mentions the following in his post: “I am also not aware of any VASA 2.0 requirement that restricts the number of PEs for a storage system’s support of a single vSphere cluster”. And I can confirm that VMware did not limit the number of Protocol Endpoints in any shape or form. I read the specifications and it literally states 1 PE at a minimum and preferably more. Note that vendor implementations of VVOL may differ, I have seen implementations that describe many PEs per storage system, but also implementations which have 1 PE per storage system. And in the case of 1 PE per storage system can that be a bottleneck?

The queue depth of the Protocol Endpoint isn’t limited to 32 like a regular LUN when multiple VMs are contending for IO (“disk.schednumreqoutstanding”) or 64 (typical device queue depth) but set to 128 by default. This can be increased when required however. Before you do, please consult your storage vendor. There are a couple of variables that need to be taken in to account like the max device queue depth for instance and then there also is the HBA max queue depth as well. (For NFS queue depth is no concern typically.) The potential constraint when there is only (uncommon) a single PE can be mitigated. What is important here is that VVOL itself does not impose any constraints.

I am hoping that clears up some of the misunderstandings out there.

Startup introduction: Springpath

Last week I was briefed by Springpath and they launched their company officially yesterday, although they have been around for a long time. Springpath was founded by Mallik Mahalingam and Krishna Yadappanavar. For those who don’t know them, Mallik was responsible for VXLAN (See the IETF draft) and Krishna was one of the folks who was responsible for VMFS. (Together with Satyam who started Pernix Data) I believe it was early 2013 or end of 2012 when Mallik reached out to me and he wanted to validate some of his thinking around the software defined storage space, I agreed to meet up and we discussed the state at that time and where some of the gaps were. Since May 2012 they operated in stealth (under the name Storvisor) and landed a total of 34 million dollars from investors like Sequoia, NEA and Redpoint. Well established VC names indeed, but what did they develop?

Springpath is what most folks would refer to as a Server SAN solution, some may also refer to it as “hyper-converged”. I don’t label them as hyper-converged as Springpath doesn’t sell a hardware solution, they sell software and have a strict hardware compatibility list. The list of server vendors on the HCL seemed to cover the majority of big players out there though, I was told Dell, HP, Cisco and SuperMicro are on the list and that others are being worked on as we speak. This approach offers a bit more flexibility according to Springpath for customers as they can chose their own preferred vendor and leverage the server vendor relationship they already have for discounts but also maintain similar operational processes.

Springpath’s primary focus in the first release is vSphere, which knowing the background of these guys makes a lot of sense, and comes in the shape of a virtual appliance. This virtual appliance is installed on top of the hypervisor and grabs local spindles and flash. With a minimum of three nodes you then can create a shared datastore which is served back to vSphere as an NFS mount. There are of course also plans to support Hyper-V and when they do the appliance will provide SMB capabilities and for KVM it will use NFS. But that is on the roadmap right now, but not too far out according to Mallik. (Note that support for Hyper-V, KVM etc will all be released in a different version. KVM and Docker is in Beta as we speak, if you are interested go to their website and drop them an email!) There is even talk about supporting the Springpath solution to run as a Docker container and providing shared storage for Docker itself. All these different platforms should be able to leverage the same shared data platform according to Springpath, the diagram below shows this architecture.

They demonstrated the configuration / installation of their stack and I must say I was impressed with how simple it was. They showed a simple UI which allowed them to configure the IP details etc, but they also showed how they could simply drop a JSON file in there with all the config details which would then be used to deploy the storage environment. When fully configured the whole environment can be managed from the Web Client, no need for a separate UI or anything like that. All integrated within the Web Client, and for Hyper-V and other platforms they had similar plans… no separate client but all manageable through the familiar interfaces those platforms already offer. [Read more…]