Non-recoverable Read Error Rate
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What Happens If The Array Experiences A Ure During The Rebuild Process?
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Unrecoverable Read Error Nero
from "example.com"url:textsearch for "text" in urlselftext:textsearch for "text" in self post contentsself:yes (or self:no)include (or exclude) raid 5 ure calculator self postsnsfw:yes (or nsfw:no)include (or exclude) results marked as NSFWe.g. subreddit:aww site:imgur.com dogsee the search faq for details.advanced search: by author, subreddit...this post was submitted on 12 Aug 20154 points (83% upvoted)shortlink: remember mereset passwordloginSubmit a new linkSubmit a new text postzfssubscribeunsubscribe1,538 readers~3 users here nowcreated by bbatsella community for 6 yearsmessage the moderatorsMODERATORSbbatsellerimar77
Working in 2009 - Not Necessarily By Darren McBride Share: Could you write and then read an entire 3TB drive fivetimes without an error? Suppose you were to run a burn in test on a brand new Seagate 3TB SATA drive, writing 3TB and then
Hard Drive Ure
reading it back to confirm the data. Our standards are such that if a drive fails ure raid 5 during 5 cycles we won’t ship it. Luckily, all 20 of 20 drives we tested last night passed. In fact, most of the 3TB unrecoverable read error rate ssd drives we test every week passed this test. Why is that a big deal? Because there is a calculation floating around out there that shows when reading a full 3TB drive there is a 21.3% chance of getting an https://www.reddit.com/r/zfs/comments/3gpkm9/statistics_on_realworld_unrecoverable_read_error/ unrecoverable read error. Clearly the commonly used probability equation isn’t modeling reality. To me this raises red flags on previous work discussing the viability of both stand alone SATA drives and large RAID arrays. It’s been fiveyears since Robin Harris pointed out that the sheer size of RAID-5 volumes, combined with the manufacturer’s Bit Error Rate (how often an unrecoverable read error occurs reading a drive) made it more and more likely that you would encounter an error while trying https://www.high-rely.com/blog/why-raid-5-stops-working-in-2009-not/ to rebuild a large (12TB) RAID-5 array after a drive failure. Robin followed up his excellent article with another “Why RAID-6 stops working in 2019” based on work by Leventhal. Since RAID-5 is still around it seems Mark Twain’s quote “The reports of my death are greatly exaggerated” is appropriate. Why hasn’t it happened? Certainly RAID-6 has become more popular in server storage systems. But RAID-5 is still used extensively, and on 12TB and larger volumes that Robin predicts don’t recover well from drive failures. Before I get into some mind numbing math let me give away what I think might be an answer: Because the Bit Error Rate (BER) for some large SATA drives are clearly better than what the manufacturer says. The spec is expressed as a worst case scenario and in the real world experience is different. Seagate’s BER on 3TB drives is stated as 10^14,but may be understated. Hitachi’s bit error rate on their 4TB SATA drives are 10^15 and in my experience the two drives perform similarly from a reliability perspective. That order of magnitude makes a big difference on the calculations of expected read errors. Let me set the stage by going back over the probability equation used by Robin Harris and Adam Leventhal. The probability equation they use for a successful read of all bits on a drive is (1-1/b)a “b” = the Bit Error Rate (BER) also known as Unrecover
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