Flash storage: real-world pros and cons

Flash memory technology has fundamentally changed the nature of computing devices, from smartphones to data centres.

Flash memory storage, once an expensive niche technology, is now well and truly in the mainstream, used in everything from smartphones to data centres. It has been replacing HDD technology for years now, because on a dollar-per-input/output basis it is far more beneficial to use.  It’s all about random and sequential read/write speeds, latency and bandwidth. And while the advantages of flash/SSD can certainly vary depending on the metric, they are far faster than hard disks, which have not scaled in performance in the same way CPUs have over the years.

“Computing is a key demand driver given SSD’s inherent benefits of fast access times, particularly for data centres where everyone wants access to data fast,” said Joe Unsworth, research vice president, semiconductors, with Gartner.

“I would say most data centres are using SSDs today, whether it be a small amount of SSD - for hot data, readily accessible data - or large pools of SSD for analytics, web searches, OLTP, financial trading and so on,” added Unsworth. “From a PC perspective, anyone using a MacBook Air no longer has a HDD in it. Any media tablet out there never came with a HDD - they come with flash.  Everyone’s smartphones are based on flash.”

It’s not all pros though; there are some cons too. Flash is far slower in sequential programming than in its random access performance; it has a finite life and therefore must be managed or it can wear out in highly write-intensive environments; and flash is expensive compared to HDD on a dollars-per megabyte basis (once all the surrounding electronics are taken into account).

Simplification

Knox Grammar School is one of Sydney's best-known independent schools, catering for almost 2500 students. Classrooms are equipped with the latest technologies and the school maintains a one-to-one student-to-laptop ratio. Currently in the process of an IT transformation, the student environment is primarily Mac-based.

Storage is refreshed or replaced every five years, while three years into each cycle the IT department reviews requirements to see if more storage if needed. “We don’t buy five years in advance because we don’t need that capacity straight away,” said Mike Israel, IT manager.

In early 2014, Israel embarked on the school’s latest storage review. “We’d got to the point where we needed to expand. We were also looking to use the review to improve our DR [disaster recovery] measures,” said Israel.

At the time, the school’s DR plan was based on off-site backups - data from the prep school was backed up to the senior campus, and vice versa. While it gave some protection, Israel noted, “We didn’t have any hardware or real standby facilities.”

Datacom recommended the school deploy a Nimble Storage CS240 array on each campus, with full replication between the devices. Although Datacom offered to manage deployment, the IT department chose to undertake the process in-house.

“We really liked the design of Nimble’s technology and the use of flash storage to speed up responses,” Israel noted. “The hardware replication was good and so was the compression.”

The arrays now have all the school’s storage for its virtual environment, databases and applications.

The ability to manage in the face of a disaster has been further boosted with the implementation of VMware Site Recovery Manager. “This is one of the main benefits of having hardware replication - VMware SRM hooks into the Nimble system and uses the hardware to seamlessly control fail-overs,” said Israel’s colleague Andrew Cullen, IT infrastructure manager.

The flash storage solution makes it “very easy to clone virtual machines, set up test environments or access old snapshots of servers or data … [and] we’ve found we can spread the burden and involve other IT staff when making changes on the system,” added Cullen. “We couldn’t do this before because our old storage systems were a little too complex.”

Flash in the cloud

Cloud service provider Hosted Network primarily sells through partners and other IT organisations that don’t have the technical expertise or skills to set up their own cloud offering. Its core offering is desktop-as-a-service.

“We partnered with VMWare a little over a year ago. We were one of four partners in Australia to stand up the offering and we were the only partner to target the other services providers, such as managed service providers and IT integrators,” said Ben Town, Hosted Network’s managing director.

“When we started to look at what we might do with our virtual desktops in a multitenanted workload, we looked at all of the different storage vendors. They all provide flash arrays and you get lots of performance,” added Town. “That’s all well and good I guess if you’ve got one application, but in our case because we’re doing thousands of desktops and lots of different customers, we needed something that would put the bounds around the performance so that one customer couldn’t impact the next.”

Hosted Network chose to go with a SolidFire offering for its flash storage. “You get that all-flash performance, but it also provides us that security and peace of mind that one customer can’t impact the other,” said Town, referring to the ‘noisy neighbour’ syndrome. “As a service provider, you don’t really have a lot of visibility into your customer’s workloads and what they are doing, because you’re providing an infrastructure and then you hand that over to them to do what they will. So we need to protect one customer from the other.

“Because we’re working through the channel, our margins are tighter, so we were also looking for something that was simple. We’re a small cloud provider, so we didn’t want to have to hire dedicated storage staff. I wanted my general support staff to be able to deal with the storage side of it, and that’s basically what we can do now. It’s very, very easy, simple to manage,” Town added.

Because it is also ‘scale out’, the company doesn’t have to worry about having lots of different arrays, and potential failures within them. “All of the other competitors within the Australian market are still using the old dual controller architecture,” said Town. “If you’re hosting a website and it goes down, well, maybe a few people will notice. But when you’re hosting someone’s entire business like we are, as soon as something goes wrong, everyone notices. So we wanted the reliability that the scale out distributed approach provides.”

“We don’t have to worry about balancing workloads within the array itself; it just deals with that. If one customer needs more performance, we tune a few things very quickly - two seconds’ worth of changes - and they can get more performance. Same with scaling back,” said Town.

“One of our use cases is a registered training organisation,” said Town. “They might be training 30 people at a time, so they need to spin up their desktops, then spin them down. We can allow them to have extra resources when they’re doing that.”

So how does Town compare operating a flash-based system versus a disk-based system?

“It’s a different way of thinking, it really is,” he said. “Storage, I guess, was an expertise before, whereas now for us it’s just a commodity. For us as a service provider, it’s fantastic. We use it as a selling point to other IT organisations - they generally know the headaches, so we can confidently go to them and guarantee them that they’re going to get the performance, because we know that the system is capable of handling it.”

The next storage technologies

But nothing stands still in the world of computing, and manufacturers are already looking to the world beyond flash. What’s coming next?

“Emerging memory technology takes at least a decade to get to market and mass produce,” said Unsworth. “First, there is 3D NAND Flash, where it has multiple layers to achieve greater density - this is in mass production already by Samsung, but it’s really nascent technology. It will carry us into 2020 and beyond, but next-generation memory technology would be a battle between memristors, phase change memory, carbon nanotubes and spin torque MRAM.”

“It will take some time and nothing will have the volume in the near-term for widespread displacement of flash until post 2020, but rather [it will] be used in the coming years as a non-volatile cache to complement NAND Flash,” added Unsworth. “Memristors shows the most promise from the specs, but that is not the same as making millions of the devices.”