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Flash storage performance changing the rules

The ability to measure flash performance requires different metrics, along with a better understanding of applications, which can make it more complicated to purchase than HDDs.

The rise of flash in storage arrays is changing the characteristics buyers look for when evaluating storage. Solid-state drives (SSDs) are often purchased for different uses than hard disk drives, and demand different buying metrics.

Flash capacity plays second fiddle to the need for speed, quality of service and data reduction. Because of SSDs, flash storage performance expectations were raised for IOPS and throughput, and latency requirements have dropped from milliseconds to microseconds.

"One requirement I want is not just more capacity, but performance," said Albert Fuller, IT manager at the San Francisco-based California Public Utilities Commission (CPUC) and a SolidFire all-flash array customer. "I need more resources more than I need capacity. I look at IOPS. If I have a SQL Server, can I add IOPS on the fly, without shutting down the system? If I want to set up one virtual machine in production and run it, I need 500 IOPS for it to be functional. If I want to increase it to 1,000 IOPS, I need to do it on the fly."

George Crump, analyst with Storage Switzerland LLC, said flash storage adoption started as a point solution to solve specific performance problems. That was phase one of flash adoption.  Now, it's evolved into a general-purpose storage medium and flash storage performance expectations have soared.

"We are now in the middle of the second phase of flash adoption: flash as a general-purpose storage system," Crump wrote in a Nov. 20 blog post on flash performance. "In this phase, all the flash arrays store all active data sets and workloads. We are also beginning phase three. In this phase, users are expecting flash performance. As a result, applications and environments are designed counting on flash storage performance. Since both phases one and two replaced hard-disk systems, the euphoria was easy to deliver."

Learn why Storage Switzerland's George Crumps says all-flash storage array purchasers will have to choose between performance and function.

Latency, throughput and IOPS have not only improved with flash, but they have become more nuanced. IT administrators need to take a different approach to understanding the metrics behind SSD and flash storage performance.

"People don't understand flash. They still think in terms of spindles," said Eric Carey, CIO for Valley Health System in Ridgewood, N.J., and a Violin Memory all-flash array customer. "The mathematics are completely different. It's not just plug-and-play. You need experience in flash or you won't get your money's worth."

IT administrators need to take a different approach to understanding the metrics behind SSD and flash performance.

Flash and SSDs often require a more thorough understanding of the application. For instance, the speed of an IOPS request is important when the data that is being requested is small in size. But when the application is large file-oriented, throughput is the key performance metric.

"When you are asking for a small file, then throughput is not the correct measurement," said Arun Taneja, founder of the analyst firm Taneja Group Inc., in Hopkinton, Mass. "For a 4K block, IOPS is more important. For a 128 KB, then throughput is more important. The one thing flash has done is speed everything up. IOPS and throughput have gone up. Latency is reduced. The biggest change has been latency, then IOPs, and then throughput."

The increase in performance also impacts the way applications are designed, Taneja said.

"Applications have to be much tighter to use flash more effectively," he said. "With flash, all expectations have gone up and it's starting to have repercussions on how we develop applications. The larger issue lurking is you don't design an application the way SAP was designed 20 years ago. Back then, you could develop an application and you knew, as a program, the answer came back in 50 milliseconds. With flash, you get a response in microseconds, so your program better be ready."

Next Steps

What's the key to optimum flash performance?

Developments in flash storage capacity and performance

Flash performance hindered by the I/O blender effect

Dig Deeper on All-flash arrays

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What do you consider the most important feature when evaluating flash performance?
Interesting points to consider. Being able to understand the pros and cons lets us make a wise choice in our media.
It seems to me that in a year or two, we're going to have a whole lot of unhappy IT guys who bought flash without understanding what they were doing or how to use it properly. That's going to be interesting.
Lately I have been reading issues that their lifespan is not as good as the old standard HDD's. I guess we will have to wait and see once it becomes more mainstream.
Hello, ToddN2000 -- actually a lot of industry statistics today show that flash is as durable and reliable as HDDs--in some cases exceeding MTBF stats of hard disks. Solid-state vendors have made terrific strides in flash controller technologies and the firmware that handles how data is written to flash. Endurance and reliability have become much less of an issue than they were just a couple of years ago.
Are we getting those statistics from anybody besides flash vendors?
Yes. There's plenty of evidence available from a variety of sources--including users. Some studies have actually shown that flash has a lower BER than hard disks. Of course, tape has the best BER...
It would be a nice test to do something like this. Load the same files to HDD, SDD /Flash, and Tape. Then do not use the media for years. Somewhere like 10 or so. Then see if the data can be extracted the cleanest. I know I have some old VHS video tapes that will not even play anymore.. It may be the media or the way the media was stored. Environmental issues may come to play with temperature and moisture.
Hey, ToddN2000, do you have 10 or so years to spare? :-) Seriously, I think you make a good point about endurance over time. I can remember hearing stories about backup tapes that became unreadable because they were dropped or somehow damaged. I fielded a survey about tape some years ago and the biggest complaints were about unloadable or unreadable cartridge. Tape has come a long way since the days of DLT, SDLT, DAT, AIT, etc. The LTO format has done a lot to make tape a much more stable medium. That said, it's still mechanical, as are HDDs, and whenever there are moving parts there's a greater likelihood of something malfunctioning. That would suggest that flash, with no moving parts, would be great for long-term retention. That is, if price wasn't a concern.
I'm definitely seeing a drop off in SSD performance, regardless of the vendor, drive usage, etc. Still, to me, even if the benefits are more short-term, the time saved and efficiencies earned more than pay for themselves with SSDs.
Yes--the drop off from a brand new flash device to one that's been used a bit can be pretty significant. The new device doesn't have to do any program/erase on write because it's essentially blank, but the more the device is written to, the more it becomes necessary to do program/erase chores. A lot of vendors are trying to mitigate this effect by over provisioning--effectively providing more capacity than what you bought and then doing the garbage collection in the background on the "extra" flash so that new writes aren't so impacted.
Yes, and that's the sort of thing I'm worried about. We seem to have pretty much quit talking about it as an issue, and I'm wondering what sort of time bomb we're creating for the future.