Storage Soup

Jan 23 2015   12:48PM GMT

NetApp: No SSDs have worn out

Carol Sliwa Carol Sliwa Profile: Carol Sliwa

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The prospect of flash drives wearing out is a non-issue, according to NetApp.

Mark Welke, NetApp’s senior director of product marketing, said the company has not had a single solid-state drive (SSD) wear out since it began selling flash with its storage systems in late 2008.

“We’re typically seeing an average of about a 10% lifetime wear for all of the SSDs that we have out there today,” said Welke, during an interview this week with SearchStorage.com. “So, I think that a lot of the hype that was created out there [about SSDs wearing out], it just doesn’t exist.”

The SSD wear-out factor stems from the process of writing data to a NAND flash chip. All of the bits in a flash block must be erased before the write can take place. That program/erase process eventually breaks down the oxide layer that traps the electrons at the floating-gate transistors. The deterioration can distort the manufacturer-set threshold value at which a charge is determined to be a zero or a one and result in errors.

That’s a condensed version of the way experts described the inner workings to me in 2009 when flash was coming into vogue. They said the deterioration was less of a problem with single-level cell (SLC) flash than with multilevel (MLC) flash. The wear-out figures they cited were 100,000 program/erase cycles for SLC, 30,000 for enterprise-grade MLC (eMLC), and 10,000 or possibly as low as 3,000 for MLC.

Welke said NetApp started with SLC SSDs in its FAS systems and followed with varying grades of less expensive multilevel cell (MLC) drives, starting with its EF540 about two years ago. The company doesn’t make its own SSDs. NetApp purchases them from a variety of manufacturers, which have included SanDisk and Toshiba.

NetApp is able to monitor the flash environments of customers through its auto-support capabilities and database. Welke said SSD failures have occasionally happened, but they were not the result of wear-out. They were typically due to SSD firmware issues, which he said have largely been fixed.

“We’re less than 30 seconds downtime per year. There aren’t many failures,” Welke said.

So, is wear-out just a bunch of hype?

Lots of SSD manufacturers worked hard on improvements to product architectures, algorithms and controllers to boost the endurance and reliability of MLC and other flash technologies and help bring down the high cost of solid-state storage in comparison to traditional disk-based systems.

George Crump, president and founder of Storage Switzerland, likened the prospect of SSD wear-out to the impending doom predicted in the year 2000 with computers that stored year values as two digits.

“I made a comment once to a data center guy and said ‘I guess that was no big deal.’ And he looked very sternly at me and said, ‘Well, that’s because a lot of people worked a lot of hours to make sure it wasn’t a big deal,’ ” recalled Crump. “It could have been a very big deal.”

Crump said that not only have flash controller manufacturers gotten very good at handling errors and generally advancing the technology but also flash use cases have changed. He said a small amount of highly expensive flash and memory was often used for caching in the early days, with data constantly moving in and out.

“As that cache area got bigger and bigger, and eventually it led to all-flash, the amount of times that I had to turn data over went down significantly, and therefore, the cause for wear-out minimized,” said Crump.

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