Solid-state drive warranty could have usage limits

A BriForum session on getting the most out of your solid-state drives for a virtual desktop infrastructure raises interesting points about what to look for in an SSD warranty.

BOSTON -- Beware of the warranty on your solid-state drive (SSD). An SSD warranty can be similar to guarantees offered on a car, with the expiration based either on its lifetime -- or years the SSD is used -- or usage, which is when it hits a terabyte or throughput limit.

That was one of the messages this week during a BriForum conference session, "How to tell when your SSD will burn out." The purpose of the session was to give users a method for calculating how much flash they need for a virtual desktop infrastructure (VDI) project. But presenter Jim Moyle, technical evangelist for storage software vendor Atlantis Computing, also pointed out possible SSD warranty issues.

"What is important is the throughput behind the warranty," Moyle said.

While SSD manufacturers usually offer three- to five-year warranties, some warranties also expire once the SSDs hit a certain level of terabyte usage.

Moyle said that the average block size in a XenApp VDI session is 23 KB and by using that figure, customers can determine when they will hit the throughput or terabyte usage on an SSD. He calculated 150 sessions per physical host, with 8 IOPS per session. That results in 1,200 IOPS per server. If the drive is active for 12 hours (43,200 working seconds) per day, that comes to 51.8 million IOPS per day.

"If you multiply 51.8 million IOPS by the 23 KB average block size, that is 1.2 terabytes per day," Moyle said. "I know what my IOPS are and I now can find out the throughput. Now I can compare warranties on SSDs. The 23 KB is the key number. It's the number that matters. I always see 23 KB average block size for Windows workloads."

Moyle said a warranty that expires when the SSD hits 145 terabytes of use covers 120 days under the above scenario.

"So instead of five years, you have four months," he said.

Moyle also pointed out that SSDs will throttle the speeds of writes to extend a drive's life. That surprised Mike Nelson, a solutions architect for cloud provider nGenx Corp.

"When you hit a terabyte limit, [do] they start throttling your writes?" Nelson asked during the session. "I had no idea that existed. So the five-year warranty really doesn't mean anything. You can go with a three-year warranty because it's cheaper. Your drive actually will expire before the three years is up."

Not all SSD array vendors place a usage limit on their warranties. Representatives of all-flash array vendor Pure Storage and hybrid array vendor Nimble Storage at BriForum said their guarantees are based only on years, not terabytes.

Paul Frisoli, senior sales engineer at Nimble, said his company's maintenance plan overrides the manufacturer warranty. "Nimble takes ownership of all hardware and software under our maintenance for the life of the system," he said. "[For] one to five years, we have your back."

According to Dennis Martin -- whose Demartek Labs tests SSD devices -- vendors are "testing the water" with limits on SSD usage under warranty.

"Some, but not all, flash vendors are tying a write or life metric to their warranties," Martin wrote in an e-mail. "This is not unlike the car companies that have five-year/60,000 mile warranties.

"This type of warranty may be perceived as a weaker warranty than the straight five-year warranty that other SSD vendors offer. The warranties of this type will include some number of terabytes written over time … or some multiple of the drive capacity written over time."

Martin said warranties with terabyte limits could show up for SSDs and PCIe cards that are designated "read-intensive."

"Obviously, the read-intensive drives aren't expected to be deployed in environments that are write-heavy, and therefore might be the type of drives that have the terabytes-written limits attached to the warranties," he wrote.

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