Non-recoverable Read Error
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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 10-15, SSD BERs range unrecoverable read error rate from 10-16 for consumer drives to 10-18 for hardened enterprise drives. Below the fold,
What Happens If The Array Experiences A Ure During The Rebuild Process?
a look at his analysis of the impact of this difference of up to 4 orders of magnitude. When a raid 5 ure calculator 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 the failed drive. If an unrecoverable read error why not to use raid 5 (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 during reconstruction was going up, and thus so was the probability of
Hard Drive Ure
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. Well, yes, but RAID-5, and RAID in general, is just one rather simple form of erasure coding. There are better forms of erasure coding for long
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 unrecoverable read error nero run a burn in test on a brand new Seagate 3TB SATA raid 10 ure drive, writing 3TB and then reading it back to confirm the data. Our standards are such that if a
Raid 6 Ure
drive fails 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 drives we test every week http://blog.dshr.org/2015/05/unrecoverable-read-errors.html 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 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 https://www.high-rely.com/blog/why-raid-5-stops-working-in-2009-not/ 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 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 re
Community Forums > Other Sciences > Computing and Technology > We've just passed 300 Insights! View them here! What a resource! Dismiss Notice Dismiss Notice Join Physics Forums Today! The friendliest, high quality science and math https://www.physicsforums.com/threads/unrecoverable-read-errors-and-raid5.789603/ community on the planet! Everyone who loves science is here! Unrecoverable read errors and RAID5 Tags: hdd raid5 unrecoverable error ure Dec 29, 2014 #1 joema A number of popular-level articles have been published saying that http://www.futurequest.net/forums/showthread.php?t=24284 RAID5 is increasingly impractical at larger data volumes due to the chance of an individual HDD having an unrecoverable read error (URE) during the rebuild phase. I think the underlying math which produced this conclusion read error may be in error, and I'd like someone to check it. Published reasoning: typical HDDs have a URE rate of 1 in 10^14 reads (interpreted as bytes). If a 16TB 8-drive RAID5 array has a single URE, that HDD must be replaced and data rebuilt on the spare. During the rebuild no further errors can be tolerated else the entire array is bad. Apparent mathematical reasoning: 1 URE per 10^14 bytes / unrecoverable read error 8 HDD per array = 1 URE per 12.5 TB read from the 8-drive array. Conclusion: given that URE rate there is a nearly 100% chance of a 2nd HDD failing while rebuilding the 16TB array. Example article: http://www.zdnet.com/article/has-raid5-stopped-working/ I think this is incorrect for several reasons: (1) Common sense: if the chance of a URE is 1 per 12.5 TB read, large RAID0 and RAID5 arrays would be failing at an incredible rate. (2) The specified URE rate is 1 per 10^14 *reads*, not bytes. Modern drives do reads in 4k-byte sectors, not bytes or 512-byte sectors. So translated to bytes, the URE rate is 1 per 10^14 * 4096 bytes per sector, or 1 URE per 409,600 terabytes read. (3) While number of drives in the array increases chance of an individual failure per unit of *operating time*, they do not increase failure chance per data transfer volume vs a single HDD of equal capacity. E.g, if reading the *same* data volume from a single HDD vs an n-drive RAID array, each drive in the array will only do 1/nth the reads, hence have 1/nth the failure chance per aggregate volume of data. Therefore for a given number of reads, the URE probability is about the same between a single drive a
In Options Calendar Search Forums Advanced Search Posts In Last Day Last 2 Days Last 3 Days Last 4 Days Last 5 Days Last Week Last 2 Weeks Last Month Last 6 Months Last Year Go to Page... Thread Tools Search this Thread Display Modes 09-15-2008, 12:16 PM Postid: 170153 Jeff Site Owner Forum Notability: 872 pts: Dignified Competence! [Post Feedback] Join Date: Jun 2000 Location: Great Lakes Posts: 4,234 Real world harddrive nonrecoverable read error rate Is the spec nonrecoverable read error rate a factor for you when buying a harddrive nowadays? What are your thoughts on upgrading from a hard drive with a nonrecoverable read error rate of <1 in 10^15 bits read to the new Seagate 1.5 TB perpendicular recording drives which have a specified nonrecoverable error rate of 1 per 10^14 bits read? Will a hardware RAID controller help with nonrecoverable drive errors? __________________ Enjoying little gasparilla island Jeff View Public Profile Visit Jeff's homepage! Find More Posts by Jeff « Previous Thread | New Threads | Next Thread » Currently Active Users Viewing This Thread: 1 (0 members and 1 visitors) Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Search this Thread Advanced Search Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts vB code is On Smilies are On [IMG] code is On HTML code is Off Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home FutureQuest Site Owners (All may read - Only Site Owners May Respond) News & Announcements Notices & Alerts Security Alerts Questions & Suggestions General Site Owner Support (All may read/respond) Open Discussions General FutureQuest Hosting Support FeatureQuest App Manager Email & Mailing List Management General Coding/Development PHP, Perl, Python and/or MySQL Domain Names & Procedures Web Site & Graphic Design FutureQuest Reviews & Kudos E-Commerce Site Promotion Resellers & Affiliates Utilities / Scripts / Software Contract or be Contracted General Computing Places To Go Sites To See! All times are GMT -4. The time now is 04:36 PM. Forum Home - Guidelines - Mark all Forums Read - Archive - FutureQuest, Inc. - Privacy - Top Running on vBulletin Copyright © 2000 - 2016, Jelsoft Enterprises Ltd. Hosted & Administrated by FutureQuest, Inc. Images & content copyright © 1998-2016 FutureQuest, Inc. Follow @FutureQuest