Before OpenStack Summit, I interviewed Mike Perez about what's new in Cinder in the LIberty release, and what's coming in Mitaka. Unfortunately, life got a little busy and I didn't get it posted before Summit. However, with Liberty still fresh, this is still very timely content.

In this interview, Mike talks about the awesome new features that have gone into Cinder for Liberty, and what we can expect to see in April.

If the audio player below doesn't work for you, you can download the full audio HERE. See also the complete transcript below.

Rich: Today I'm speaking with Mike Perez, who is the PTL of the Cinder project. Cinder has been around for …

Mike: Since the Folsom release.

R: So, quite a while. Thanks for taking time to talk with me.

I wonder if you could start by giving us a real quick definition of Cinder. I know that people who are new to OpenStack are frequently a little bit confused as to what it is, and how it differs from Swift and various other storage type things that are part of OpenStack.

M: Cinder, just like a variety of other OpenStack projects, is just an API layer. So unlike other projects like Swift, for example, which is an actual implementation of a type of storage, that's where there would be a little bit of a difference right there.

In particular, Cinder is more interested in providing block storage, as opposed to object storage. They have differences in terms of how exactly you interact with retrieving the data, as well as adding data to it, and then they also support different types of use cases. In particular, just without Cinder or Swift in the picture, if you just have your OpenStack cloud with Nova and Neutron, you just have ephemeral storage that you're using with your instances. Typically, with those type of setups, your storage goes away as soon as the instance goes away. Adding Cinder into the picture, though, you are given the ability to have persistent storage, so that the storage itself becomes completely independent of the actual virtual machine instance. So when you terminate your virtual machine instance on the Nova side, there will be a detach of that block storage volume, and then you can later on attach it to another virtual machine instance.

R: Tell us about Liberty. What's new in Cinder?

M: Inside of the Liberty release we have 16 new volume drivers. They're all backed with Cinder continuous integration testing that we adopt from Tempest. Cinder has one of the most - I would say - the most drivers out of the OpenStack projects. We're just shy of around 60 volume drivers now. Some of them are from multiple vendors. As I mentioned before, they are all backed behind the continuous integration, so we know for a fact, as we are going through a development cycle in Liberty, these volume drivers, the actual back-ends themselves, are being tested. Every single vendor is expected to have a CI system in their own lab, hooked up to a real storage solution that they are trying to support inside of Cinder. That patch will bring us - they're expected for their CI to bring up a CI instance that connects to that storage back-end and runs their Tempest tests, and verify that that patch doesn't break their integration with their volume driver. That came back in the Kilo release. The story's in a lot of different places. It was a lot of fun getting us to that point. It's been nice talking to other projects, because I know a lot of other projects are interested in going down the same path, and it's been great having discussions with a variety of other PTLs on it.

And along with that we added in support for image caching. You have an image inside of Glance that you want to boot up a VM with that image. And with Cinder in particular, since the storage itself is in some other remote location from that virtual machine, because we're attaching over something like ISCSI or fibrechannel, grabbing the image from wherever Glance is at, whatever Glance store is set up with Glance itself - could be inside of Swift for example, you have an image inside of Swift - and you want to put that image onto a newly allocated space volume inside of Cinder, in order to do that, it has to go across the network to whatever storage solution Cinder is set up with, and that can be really time consuming, especially for some of our users that are using 20-40Gb images. It can take a lot of time to boot up that VM. Cinder itself has a very generic image caching solution that we added in for the Liberty release, that allows for the most popular images inside of your cloud to be cached within the back-end storage solution. So what that means is, for that cache we can do some really smart things with the different storage solution. Instead of doing copy of the actual image, we can do copy-on-writes, for example. So it's pretty much a zero copy, you're just pointing a reference to that image that's already allocated on that storage solution. And then create a new volume off of that reference pointer. Bam! You have a new volume that is set up with that image, and there's zero copies that had to happen. I think that's going to take care of a really popular problem, that comes up, and should make users really happy for this release.

Some of the other things that we added support for that are kind of general things is nested quota support, for example. Keystone has this ability with having projects within projects. Users and operators want to be able to have the ability to set quotas based on having a hierarchy for quotas. I'm not sure about other projects, but Cinder has added this in now for the Liberty release, so you will be able to add that with your different volume allocation, as well as your gigabyte allocation as well, for project hierarchy.

The third piece I would add in is the non-disruptive backups. Cinder has this ability for doing backups. These are different from snapshots. Snapshots, you're typically doing the actual volume itself. You're copying the entire allocation of that volume. So, let's say you have a 100G volume, and you're only using 5G of it, it's still doing a snapshot of 100G, even unused parts. The difference with a backup is you have the ability to do a backup of just the contents, what you're actually using. And on top of it you're also able to have the volume backed up to another location, let's say you could set up a Cinder backup service that is able to talk to Swift. For your Cinder side, you have Ceph set up. So you have completely two separate storage solutions, and if something were to happen to the Ceph storage solution, everything would still be backed up on this other Swift cluster that's completely independent.

The problem with doing backups, though, typically was - and this is just with block storage in general - is you would have to detach the volume from it being used by the VM, and then you would have to initiate a backup, and then reattach that volume to the Cinder backup solution which would then go ahead and put it into the Swift cluster. That could be disruptive. The new solution that now we have is, some of the different back-end solutions that we're using for the Cinder backups will give you the ability to keep the volume attached, and actively being used, but we can go ahead and initiate a backup, and it will keep copying over the bits, and hopefully eventually catch up to where the volume is at, to a point where it can stop the backups, and your volume can continue being used in production.

I would say those are the most interesting for the Liberty release.

R: What's your vision, looking forward, for Mitaka and on, for Cinder.

M: I sort of talked about this in the previous Liberty release, and unfortunately we weren't exactly able to finish everything up in time. My apologies to everyone. But for the operator side, we have been working on trying to make rolling upgrades a real thing, instead of just talking about it. Initially, for the Kilo release, we worked on a solution inside of Oslo that gives you the ability to have the OpenStack services themselves be written in a way to be independent from the actual database solution that's being used. Typically when you do upgrade you have to bring down - whatever services you're going to upgrade, you have bring down those services, and then you have to do a database upgrade. And for real OpenStack users, that can be very time consuming because of all the different column changes that have to happen for all of the different rows of data that they have. During that time, you have down time of those services. So, for the Kilo release we ended up working on a solution that made those services where they could continue running, and you could run the database upgrade and there would be no disruption. And when you found it convenient to do it, you can restart those services so that they could take advantage of the new database changes. But they could continue to run even with the database changes happening underneath. So that was added in Oslo, and we made that available for all OpenStack projects, not just Cinder, to take advantage of.

What we're working on for the M release, and what we were working on for Liberty as well, is the ability to have the services be independent of each other. The way that they communicate with each other is with RPC. For example, if you have, in the Cinder case, typical setup is you have a Cinder API server, you have a Cinder scheduler, and you have a Cinder volume manager. And as soon as you upgrade one of those services, they can no longer talk to each other. So, having the ability, as an operator, to roll out the updates to, say, all of my Cinder APIs, and verify that everything looks good, and then to make the decision, ok, now I want to update the Cinder scheduler. So it's all about being comfortable, and having things be convenient for the operator. So the RPC compatibility layer will allow the operator to do those upgrades at their own pace.

And, just like what we did with the Cinder database upgrade case, we're trying to make this a generic solution so that we can allow all OpenStack projects to take advantage of this same solution.

Very likely, just like what we did before, it will be something that will surface up into the Oslo library as well.

One feature that I know in particular that will be coming out, that has already finished in the Liberty release, but we just didn't have any of our volume drivers take advantage of it yet, is just some basic replication ability. To be able to say that I have this volume, which is the primary, and have other volumes that for that particular volume will be replicated over. And if anything was to happen to the primary volume, it would fail over to the secondary volume. So, really basic replication, and we're not trying to do all the bells and whistles out of the box right now, so it is a manual failover case. From what we've got in previous summit discussions, people were kind of OK anyways with doing manual failover. Weren't completely comfortable with trusting software to do auto-failover. Eventually we'll get over there, but I think getting all volume drivers over to supporting replication is a big win.

And then for the rest of the M release, I would say is a lot of catchup with some of the other projects in terms of the ability - this is not really something for the users, or the actual operators themselves - but the support of microversions. Just having the ability for us to progress forward in the API while still preserving some backward compatibility.

And then, the last part that I would say that may still not be something noticeable to users and operators, but we are working a lot more closely with the Nova team. In previous times there hasn't been a lot of interactions between the two teams, and Nova uses the Cinder API pretty heavily in the cases where persistent storage is needed. And I would say that currently, today, we have quite a number of issues that we're trying to work through in terms of how they're expecting to use our API, and how well we defined our API to them initially. So, I wouldn't really say it's a fault in anybody that's been using our API, but more us trying to figure out how to define to people that want to use our API how it should be used properly.
And now we're trying to clean that up as we go.

So, basically, we should see in the M release is better interaction between Nova and Cinder and, if there are any issues that happen in those interactions, that they'll be able to recover from those issues. So any time that Nova wants to create a volume and attach it, and something were fail in between there, there would be some sort of recovery that would happen, that the user can understand what just happened, and could take action from there. Because currently, today, there's really not much information for the user to go by to know what to do next.

R: Thank you very much for taking the time to do this.

M: No problem.