Virsto Makes SSDs Sing; Interview with Virsto Software CEO Davis Part IV

Everyone sings the praises of how great and wonderful private cloud infrastructures are and what a difference maker solid state disks (SSDs) are. However Virsto has found that its software provides some of the secret ingredients needed to make private cloud infrastructures easy to manage and what it really takes to make SSDs sing. Today I complete my interview series with Virsto’s CEO, Mark Davis, about what Virsto offers to bring out the best in private cloud infrastructures and SSDs.

Ben: We have talked a great deal about how Virsto addresses VDI but you also described Virsto as fitting into the private cloud storage infrastructure space. Can you explain?

Mark:  There’s a lot of overlap between the two but there are some distinguishing characteristics. In the private cloud, in addition to all the things we talked about where we want to have consistent high performance, we can also deliver quality of service (QoS).

If you’re doing a cloud, QoS is really important. If somebody wants to fire up a new virtual machine (VM), particularly if it’s in a private cloud and particularly if it is a self service private cloud where users can kind of request a virtual machine on demand, the user needs to know that when they request a VM it’s going to perform well.

You also need to know that it’s going to happen fast. The process of getting that VM operational should take no more than a few seconds. Without Virsto software, if you had to actually make a clone of a golden master every time you did that, it might take 20 or 30 minutes because that is how long it takes to copy the data.

We also want to the management of the life cycle of that virtual machine and its underlying storage to be very efficient.  Virsto is incredibly efficient and is integrated with the hypervisor as opposed to being a separate storage or virtual machine management process.

Virsto strongly believes that there is value in integrating directly into the hypervisor platform, as opposed to simply being a storage object on the other end of the cable talking to a hypervisor. By integrating directly into ESX, Virsto controls, if you will, the I/O of ESX, or the I/O of Microsoft Hyper-V.

So we not only do all of this cool performance stuff, but we also integrate into the management infrastructure in a way that’s completely seamless. If you are a VMware administrator and you install Virsto software, the training to understand our software is zero. It’s just the same.

It’s exactly what you’re used to because the provisioning process, the life cycle management process, the space reclamation process after you’re done using the virtual machine, is exactly the same.

Ben:  You say that Virsto supports all block based storage. What are you doing in the SSD space that makes it special when compared to other block devices?

Mark:  That’s a great question. I believe that SSD is a wonderful thing and the technology is amazing. I think most people use it as a blunt force instrument these days because it’s hard to use SSD efficiently.

There are frankly very few customers in the world who could really afford an all solid state solution as their storage. There is still a quite dramatic difference in the price per terabyte of storage in SATA drives versus SSD and it is going to be that way for the foreseeable future. So we need solutions that efficiently and optimally used SSDs.

There are a couple of ways in which Virsto make SSDs shine. Virsto builds into our software a tiering feature that allows the user to assign the log that I described to an SSD. It also potentially assigns the golden images, maybe the golden master in a VDI environment, to a solid state tier.

So you can get the super high performance for writes to the log as well as reads from the golden master that are really voluminous in a VDI environment. You may then use a lower cost storage, usually SATA, but sometimes SAS or fiber channel, for the back end storage.

Customers that use Virsto’s software find that that kind of configuration can deliver every bit as good a performance as a pure SSD, pure solid state system, but obviously at a vastly lower cost. The other thing we do by the way that is particularly SSD friendly is the way we do I/O.

This is a technical detail that probably most of your end user customers might not appreciate, but storage people understand. SSDs are not very good at random writes. In fact, they are barely faster than a spinning disk drive when it comes to random I/O which is due do a funny characteristics of the way flash is built.

Because Virsto always does sequential writes, our software does not know how to do a random write. No matter how random the I/O streams are from the guest OSes, we will make them sequential when we write them to the log. So that is why Virsto really sings when it’s combined with solid state disk for the log.

Ben:  So when you guys are in the SSD, you have to be very careful to be on the block edges and managing erasure blocks correctly and all that kind of stuff. Are you guys bothering with that or is it just mostly making sure that you get the high density of data into each block?

Mark:   It’s mostly our job to get a high density of data. You are sort of alluding to the fact that you do not want to kind of write and have what are known as write holes, these little gaps in your writes, because that’s just a total waste of time.

When you write to flash, you have to write to all blocks no matter what. Again, we always do sequential block writes as that is the only way Virsto knows how to do writes. It’s inherent within our architecture. So because we write to this log in a highly sequential there is never a write gap.

This of this log as circular. When we get to the end of the log and get to the bottom of the log writing, the data at the top of the log has already been flushed out of it and put on the back end storage. So we just go back in a circle and start writing the next trip around the loop there. So from the point of view of a flash device, we are about as perfect of an application as they could imagine.

In Part I of this interview series, we look at how Virsto creates a VMware storage hypervisor in VMware
vSphere to give incredible boosts in performance using even traditional

In Part II of this interview series, we looked at what the virtual machine I/O problem is and how Virsto fixes it.

In Part III of this interview series, we talk about where Virsto sits in the vSphere stack and how it works to deliver these increases in performance.

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