VMware's Virtual SAN Threatens Traditional Data Storage Models

Monday Mar 10th 2014 by Paul Rubens
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VMware's Virtual SAN represents a major step forward in software defined storage -- one that is surely to be met by competitors.

 VMware has launched the final part of its software defined data center puzzle: a virtual SAN product called Virtual SAN.

The product has been in beta testing for the last six months, with around 12,000 customers, but there were still plenty of surprise announcements made at the launch event on March 6.

The biggest of these was the maximum size of its Virtual SAN. Previously VMware had said that this would be 8 server nodes, and then 16. But VMware CEO Pat Gelsinger announced that the product has been upgraded to support 32 nodes.

Now for some math. Each node can host up to 32 disks and up to 100 virtual machines (VMs). That means that a 32 node Virtual SAN can host 3,200 VMs . It can also provide a maximum of 4.4 petabytes of storage space, and offer 2M IOPS (100% read) .

"This is a monster," said Gelsinger, echoing the monster VM concept that the company introduced in 2011 with the introduction of vSphere 5. "This will take care of the storage requirements of pretty much any enterprise, and they don't need to deal with any hardware underneath."

He added that performance scales linearly - a 16 node setup offers 1M IOPS, a 32 node one offers 2M IOPS - and despite his previous comment about 32 nodes being monstrous, he hinted that even larger Virtual SANs are on the roadmap: "There will be more in the future. Just you wait."

So how does Virtual SAN work and what makes it different from other virtual storage products from the likes of Nutanix or Nexenta? The key difference is that most virtualized storage systems require a storage hypervisor or virtual storage appliance running on top of VMware's hypervisor, alongside virtual machines, or some other software.

This can cause problems with resilience and performance, which VMware's solution avoids, according to Ben Fathi, VMware's CTO.

"We have built Virtual SAN into the hypervisor, so there is no special software to install and maintain. You just install vSphere," he explained.

Being embedded in the kernel of the hypervisor means Virtual SAN is uniquely positioned in the software stack for visibility into applications. It also has a unique view of the infrastructure beneath it that allows it to optimize the I/O data path to deliver better performance than a virtual appliance or external device, he claimed.

"It takes disks and SSDs and abstracts them, and pools them as a shared storage tier, and you can put VMDKs on them," he continued. "You no longer have to deal with the underlying hardware, LUNs, fibre channel - you don't need to bother with any of that."

Fathi specifically mentions SSDs, and in fact it is a requirement of every node that it contains at least one SSD. The reason for that is that the inclusion of SSD storage allows applications to be optimized to run faster, and it also allows nodes to be rebuilt faster in the case of a hardware failure. The SSDs themselves don't affect the storage capacity of each node - 30% of their capacity is used as a non-persistent write buffer, and 70% is used a read cache.

The next question is: how do you build a Virtual SAN?

It turns out that there's two ways. The first way is to buy VSAN Ready Nodes or VSAN Ready Blocks from a VMWare partners such as Cisco, Dell, Fujitsu, IBM and Supermicro.  A Ready Node is a single tested pre-configured server and a Ready-Block is a tested pre-configured set of servers for use with Virtual SAN. They include controllers, disks, and SSDs and are ready to plug in and run.  

The other way is to build your own nodes by choosing individual components from the Virtual SAN Compatibility Guide: any server on the vSphere Hardware Compatibility List, at least one multi-level cell SSD (or better) or PCIe SSD, at least one SAS/NL-SAS HDD or select SATA HDD, and a 6Gb enterprise grade HBA/RAID controller.  (Nodes which don't contribute any storage resources can also be added to a cluster to improve compute performance for the cluster as a whole.)

How much will they cost? At the moment that’s the $64,000 question because Gelsinger didn't provide any pricing details at all. Reports of license costs leaked on the Internet suggest that a Virtual SAN license may costs around $750 per CPU, and if you estimate a server cost of about $5000 - $6000, with an extra $5000 or so for SSD and HDD drives, you get an all in per-node price of about $11,000 to $12,000.

That would make a 3 node cluster come in at around $35,000, and a large 32-node cluster would cost around $370,000.

Once you have your Virtual SAN up and running, it is integrated with the rest of the VMware software stack. That means that you can do most of what you can do with traditional storage. That includes vMotion, snapshots, clones, Distributed Resource Scheduler (SRS) , vSphere High Availability (vSphere HA),  vCenter Site Recovery Manager (vCenter SRM) and more.

There is one caveat thought - there is no talk about deduplication or compression as  features  of Virtual SAN (yet.) These are features that other virtual SAN providers offer, and ones that many customers are likely to want. Getting those features will costs extra until they are provided in a possible future upgrade.

One of the features that Gelsinger was very keen to mention was simplicity, and the company showed that once the hardware is in place with vSphere running on top of it, it is remarkably easy to get a Virtual SAN up and running.

The first step, from vCenter, is to turn on the Virtual SAN feature. Then you need to allocate disks to the Virtual SAN pool, and this can either be done manually by selecting them, or automatically - the software finds all unused disks and adds them to the pool and adds any new ones when they come online.

The next is setting up storage policies (similar to quality of service (QoS) levels). These policies lie at the heart of how the Virtual SAN operates, allowing VM and application storage requirements such as high availability of performance to be defined.

For example, you can pick the number of node failures to tolerate. If you pick 1, then Virtual SAN makes two copies of each piece of data; if you pick 2 then it makes 3 copies on three separate nodes, and so on.

Another option might affect performance - for example setting flash read cache reservation to 10%.

These two settings (and others) can be saved as a storage policy, which can then be applied to an application placed on the Virtual SAN.

From that point on Virtual SAN tries to ensure that the application is run according to that storage policy, remediating automatically if anything makes the application fall out of compliance with the policy (providing sufficient resources are available.)

For example, if one of the nodes in the Virtual SAN fails then the software automatically makes a new copy of the data and places it on another node so that there are still the required number of copies of the data.

This simplicity is significant in what it implies for storage professionals, according to Mark Peters, senior analyst at Enterprise Strategy Group. "It  means non-storage specialists can run storage, and don’t need to attend in-depth training to do so."

The key benefit to enterprises implementing Virtual SAN is cost savings, Peters believes. "Virtual SAN is a tightly integrated plug-and-play investment, where maintenance and operations are simplified because there are no issues with third-party API integrations," he says.

Further savings stem from easier infrastructure management, he adds. "There is no need for a dedicated IT administrator to deal with vendor-specific storage intricacies. An IT administrator can easily see the shared Virtual SAN storage resources, compute resources, and, most importantly, the defined storage policies, all from the familiar vSphere management interface.

This means increased efficiency and productivity for VM administrators because they will no longer need to switch between different interfaces from a multitude of vendor-specific plug-ins, or manage LUN relationships, Peters concludes.

The obvious question to ask about Virtual SAN is: how will it be used? VMware suggests that it could be used in test and development environments, as well as being suitable for virtual desktop infrastructure (VDI) implementations.

It's a use case that Gartner analyst Dave Russell also foresees. "There's no need for to rip and replace, much less a desire to rip and replace, the infrastructure you have already purchased and deployed.  So it's looking for new workloads that might be appropriate  - VDI is one example  that might be a solid fit for a new deployment," he says.

ESG's Mark Peters agrees with this assessment, in the short term at least. "(Adoption) will start fairly narrow I would imagine - partly because VMware will constrain it and partly because users will be dipping their toes," he says. "Then - as is typical with many ‘new’ approaches in this business - users will discover that wider applicability is just fine."

And that means that the introduction of Virtual SAN will have long term ramifications for the storage industry, according to Peters.  "While the functionality of the product still has room to grow, the simplicity and economy of Virtual SAN represents clear writing on the (software-defined data center) wall that traditional storage models are under threat," he concludes.

Virtual SAN quick facts:

· Virtual SAN available the week of the 10th of March

· Virtual SAN supported in vSphere 5.5 Update 1 and later

· Support for up to 32 hosts (nodes) in a Virtual SAN

· Support for up to 3200 VMs in a Virtual SAN

· Support for VMware Horizon / View

· Linear Scalability for capacity and performance

· 2 Million IOPS (read only)

· 4.4 PB  maximum storage

· Free 60 day trial available from VMware, go to VMware Virtual SAN.

Photo courtesy of Shutterstock.

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