Comment by bluegreyred | Hacker News Reader

Comment by bluegreyred | Hacker News Reader

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Yes, there's also the topic of unrecoverable read errors (URE) and their effect on successful RAID rebuilds. [1][2]

Most consumer drives are still sold rated as <10^14 bits read per error. That's 12.5 terabytes, so in the worst case you could end up in situations where — on average — you are unable read a full 16TB drive without an error. Needless to say this is less than optimal for rebuilding a failed RAID array.

Anecdotal evidence (i.e. very low error rates during ZFS scrubs) suggests that manufacturers underrate their drives and they are much more reliable than that, but it is something to keep in mind.

Fortunately drive capacity completely outpaced my needs for personal data storage in the recent years, so I am happy with JBOD or RAID1, with backups of course.

[1]http://www.raidtips.com/raid5-ure.aspx [2]https://magj.github.io/raid-failure/

> Anecdotal evidence (i.e. very low error rates during ZFS scrubs) suggests that manufacturers underrate their drives and they are much more reliable than that, but it is something to keep in mind.

I've seen plenty of drives returning invalid data with correct CRC over the years. On reliable server-grade Xeon + ECC hardware. Of course the vast majority of drives never do it, there's just no way to know which ones do until it happens.

Firmware bugs in weird corner cases? Cosmic rays? Perhaps, but I think it's more reasonable just consider it one of those weird things that occasionally Just Happen (TM) and just need to be protected against at a higher level.

All drives produced in the last 30 years or so are running ever more complicated software stacks. For example they all have features that move data at risk to safer locations without the host system requesting or even knowing about it. Their physical (like bits on spinning rust or NAND flash block) and logical (what the host sees) data representations can be completely different.

Plain old CRC errors, though, are way more frequent. I feel much more comfortable about those errors, at least the drive knows the data is corrupted.

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