Hacker News Reader

Comment by cjensen | Hacker News Reader

These are Enterprise class drives.

In SSDs, the big difference between Enterprise and Consumer is endurance. Flash memory wears out over time and the firmware manages the wear and maps out bad sectors over time. Eventually, too much wears out and the drive can no longer be written to, or is too slow to usably write to. The endurance spec tells you how much data you can expect to write before the drive must be replaced.

Micron sells both consumer and enterprise drives. The consumer 1100 SSDs max out at 400TB endurance which is fantastic for a consumer drive. These enterprise 5100 drives max out at 17.6PB endurance -- that's 44X better!

If you have an application which writes a lot of data, you should be evaluating whether or not you need something like this.

View on HN

Hasn't there been an article on HN recently that showed consumer grade drive endurance testing? I believe many exceeded the endurance spec manyfold.

That was the TechReport website. Here's a link: http://techreport.com/review/27436/the-ssd-endurance-experim...

There is some uncertainty in the numbers, so the manufacturers quote fairly conservative numbers. In recent years flash cells have become a bit more fragile and the process technology has changed multiple times, so good past results on endurance testing are not necessarily indicative of future results.

I've personally burnt out a set of SSDs installed in a RAID-6. They lost no data and failed no writes, but they had become unusably slow -- less than a tenth of their original write speed.

What kind of SSDs were these, and how much writing had they been subjected to? If the flash was really wearing out, I'd expect read performance to also suffer significantly as LDPC soft decode error correction was required to recover the data intact. If only write speed was degrading and if you weren't thoroughly hammering the drives with writes around the clock, then you might merely have filled up the drives with a RAID configuration that didn't pass through TRIM commands.

If the read speed had degraded, I didn't notice since the RAID controller is the bottleneck in this particular system.

We burned out the drives with a 800Mb/s sustained 24/7 write stream. In post-mortem I did the math and the consumer drives ran out of endurance in less than a month. We replaced the drives with enterprise drives which were expected to last at least 3 years.

Also, here's a really strange finding... TRIM doesn't matter as much as one would expect. Many TRIM implementations are buggy. If the SSD contains a reliable TRIM implementation, then you can 100% guarantee that it will also have internal "move stable bits around to level out the usage" code.

Reply on news.ycombinator.com