It used to be that warranties for hard drives were for some specified number of years, it didn’t matter how much load they were under (compare SSDs). But it seems that is now changing, as capacities are pushed to the point where ever more creative strategies are needed to get the devices to work at all <http://www.theregister.co.uk/2016/05/03/when_did_hard_drives_get_workload_rate_limits/>.

Drive vendors have been bringing this metric in over the last 4 years or so, but only for new drive models, which is why it’s taken a while for people to notice. It’s really not as bad as it sounds - much like with SSDs, you’re very unlikely to ever come close to the “rated workloads” in most use cases.

From what I’ve seen so far through my work, this rating is used to explain higher-than-datasheet failure rates, rather than rejecting warranty claims . If you push a drive rated for 550TB/year beyond that level, then the failure rate increases. This is the vendor claim, and it’s something I’ve seen born out over time too - our appliances with low disk usage have a low drive failure rate overall (in some cases, better than the datasheet rating for AFR), and the ones with higher disk usage have a much higher failure rate than the datasheet AFR.

What it does do is lead you pick drive models that make sense for your workload. If you know you’re going to stick some cold data on the drive and maybe refresh it once or twice a year, the drives rated for 100-180TB/year workload are perfectly fine. If you have a moderately busy system, then drives rated at 550TB/year are probably ok. But if you are doing 500TB/year of writes and you pick a 180TB/year rated drive, don’t complain when your AFR creeps up. Overall, I think it’s a useful tool. Here’s a whitepaper from WDC on the subject: http://www.wdc.com/wdproducts/library/other/2579-772003.pdf <http://www.wdc.com/wdproducts/library/other/2579-772003.pdf>