[mrb]

The author is wrong that "enterprise quality disks just plain last longer". CMU did a study on this topic on a population of 100 thousand drives, and found that enterprise-grade drives do not seem to be more reliable than consumer-grade drives. See the conclusion in: http://www.cs.cmu.edu/~bianca/fast07.pdf This legend must die.

The author is also wrong when saying "a non-recoverable read error [is] a function of disk electronics not a bad block". An NRE can happen for different reasons, one of them is when (data and error-correction) bits in the block get corrupted in a way that prevent the error-correction logic from detecting this error. So the block is technically bad, just not bad enough to cause the drive logic to declare it as a read failure.

[akg_67]

The CMU study is most probably flawed as it looked at hardware replacement records and didn't take into consideration the different usage and threshold for replacement between enterprise and consumer drives. Most enterprise drives are used in enterprise servers and storage systems that monitor drive errors closely using SMART. The threshold for drive errors is much lower with such systems and drives are replaced quickly. My company (storage system vendor) replaces disk even when the SMART alerts impending failure and doesn't wait for actual failure. This will come across in hardware replacement log as more frequent replacement of enterprise disks. The consumer disks are used in consumer systems. The consumers don't proactively replace disks, they wait until disk actually fails. This will show up in hardware replacement log as less frequent replacement of consumer disk.

I have actually used 'defective' enterprise disks in consumer systems for years after they were labeled defective by storage system vendors. About a decade ago, I used to buy such defective enterprise disks in bulk at auction from server and storage manufacturers and sold them as refurbished disks to consumers after testing.

[mrb]

I fail to see your point about the threshold of replacement. Assuming that enterprise-class drives get replaced sooner because sysadmins monitor SMART, it is still widely acknowledged that SMART errors are a strong indicated that the drive will fail soon. For example the Google study on drive reliability showed this correlation on consumer-class drives [1] There is no reason to believe this correlation doesn't exist with enterprise-class drives (or else, what would be the point of SMART?). Therefore the replacement threshold is mostly irrelevant as the enterprise drive replaced due to SMART would have failed soon anyway.

I really don't understand this skewed perception of consumer- vs enterprise-grade harddrives. Do you believe that enterprise CPUs are more reliable than consumer CPUs? How about enterprise NICs vs consumer NICs?

Consumer-grade drives are sold in volumes so much larger than enterprise-grade drives, that vendors have strong incentives to make them as reliable as possible. I would even say they have incentives to make them more reliable than enterprise-grade drives. Because a single percentage point improvement in their reliability will drastically reduce the costs associated to warranty claims and repairs.

My own experience confirms the CMU study. I have worked at 2 companies selling each about 2-5 thousand drives as part of appliances, to customers across the world. One company was using SCSI drives, the other IDE/SATA. And the replacement rates were similar.

I can see your point about the usage being different which could invalidate the CMU findings about consumer vs enterprise drive reliability. But I don't personally believe it explains it. The CMU study + my annecdotal evidence one 2-5 thousand drives + the fact that no study has ever showed data suggesting enterprise drives are more reliable, makes me think that they are not.

[1] http://static.googleusercontent.com/external_content/untrust...