Error Unrecoverable Read Error While Reading
Contents |
the unrecoverable data error in which he points out that while disk manufacturers quoted Bit Error Rates (BER) for hard disks are typically 10-14 or unrecoverable read error while checking the game crc 10-15, SSD BERs range from 10-16 for consumer drives to 10-18 for hardened unrecoverable read error nero enterprise drives. Below the fold, a look at his analysis of the impact of this difference of up to raid unrecoverable read error 4 orders of magnitude. When a disk in a RAID-5 array fails and is replaced, all the data on other drives in the array must be read to reconstruct the data from
Raid 5 Unrecoverable Read Error
the failed drive. If an unrecoverable read error (URE) is encountered in this process, one or more data blocks will be lost. RAID-6 and up can survive increasing numbers of UREs. It has been obvious for some time that as hard disks got bigger without a corresponding decrease in BER that RAID technology had a problem, in that the probability of encountering a URE imgburn unrecovered read error during reconstruction was going up, and thus so was the probability of losing data when a drive failed.As Trevor writes: Putting this into rather brutal context, consider the data sheet for the 8TB Archive Drive from Seagate. This has an error rate of 10^14 bits. That is one URE every 12.5TB. That means Seagate will not guarantee that you can fully read the entire drive twice before encountering a URE. Let's say that I have a RAID 5 of four 5TB drives and one dies. There is 12TB worth of data to be read from the remaining three drives before the array can be rebuilt. Taking all of the URE math from the above links and dramatically simplifying it, my chances of reading all 12TB before hitting a URE are not very good. With 6TB drives I am beyond the math. In theory, I shouldn't be able to rebuild a failed RAID 5 array using 6TB drives that have a 10^14 BER. I will encounter a URE before the array is rebuilt and then I'd better hope the backups work. So RAID 5 for consumer hard drives is dead. Wel
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 makemkv unrecovered read error in test on a brand new Seagate 3TB SATA drive, writing 3TB and
Unrecoverable Read Error Ure
then reading it back to confirm the data. Our standards are such that if a drive fails during 5
What Happens If The Array Experiences A Ure During The Rebuild Process?
cycles we won’t ship it. Luckily, all 20 of 20 drives we tested last night passed. In fact, most of the 3TB drives we test every week passed this test. Why is that http://blog.dshr.org/2015/05/unrecoverable-read-errors.html 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 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 https://www.high-rely.com/blog/why-raid-5-stops-working-in-2009-not/ 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 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. Hi
All times are UTC Powered by phpBB Forum Software © phpBB Group