Raid Read Error Not Connectable
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is the best choice, ever [1]. There are cases where RAID0 is mathematically proven
Unrecoverable Read Error Rate
more reliable than RAID5 [2]. RAID5 should never be used for anything raid 5 ure calculator where you value keeping your data. I am not exaggerating when I say that very often, your data
Unrecoverable Read Error Ure
is safer on a single hard drive than it is on a RAID5 array. Please let that sink in.The problem is that once a drive fails, during the rebuild, if any what happens if the array experiences a ure during the rebuild process? of the surviving drives experience an unrecoverable read error (URE), the entire array will fail. On consumer-grade SATA drives that have a URE rate of 1 in 10^14, that means if the data on the surviving drives totals 12TB, the probability of the array failing rebuild is close to 100%. Enterprise SAS drives are typically rated 1 URE in 10^15, so raid 10 ure you improve your chances ten-fold. Still an avoidable risk.RAID6 suffers from the same fundamental flaw as RAID5, but the probability of complete array failure is pushed back one level, making RAID6 with enterprise SAS drives possibly acceptable in some cases, for now (until hard drive capacities get larger).I no longer use parity RAID. Always RAID10 [3]. If a customer insists on RAID5, I tell them they can hire someone else, and I am prepared to walk away.I haven't even touched on the ridiculous cases where it takes RAID5 arrays weeks or months to rebuild, while an entire company limps inefficiently along. When productivity suffers company-wide, the decision makers wish they had paid the tiny price for a few extra disks to do RAID10.In the article, he has 12x 4TB drives. Once two drives failed, assuming he is using enterprise drives (Dell calls them "near-line SAS", just an enterprise SATA), there is a 33% chance the entire array fails if he tries to rebuild. If the drives are plain SATA, there is almost no chance the array completes a rebuild.[1] http://www.smbitjournal.com/2012/11/choosing-a-raid-level-by...[2] http://www.smbitjournal.com/2012/05/when-no-redundancy-is-
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Hard Drive Ure
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Raid 6 Ure
it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top mdadm raid5 read error not correctable up vote 1 down vote favorite I have a software raid5 setup existing https://news.ycombinator.com/item?id=8306499 of 4 disks. sda, sdb, sdc, sdd Since everything was up and running I wanted to test the array. To do this I pulled the plug on one of the disks (sdd). Everything went fine so I tried re-adding the disk with mdadm --add /dev/md0 /dev/sdd, mdadm was rebuilding the array so after a couple of hours I checked and something went wrong, sdc failed. Long story short: sdc has some bad sectors, when mdadm reads from these sectors it fails. http://superuser.com/questions/387711/mdadm-raid5-read-error-not-correctable In /var/log/messages I can see: read error not correctable (sector 753682864 on sdc). I can not --assemble the array as it sees sdc and sdd as faulty. I can however mdadm /dev/md0 --create --assume-clean -l5 -n4 /dev/sd[abc] missing. After this I tried to add sdd but without success. When mdadm fails and it reports the sector in /var/log/messages I can verify this by executing hdparm --read-sector [sector] /dev/sdc. When I overwrite the sector using hdparm --write-sector it gets replaced and then it functions again. But this is a very time consuming process. Are there any ways how I can recover from this mess? Would mirroring sdc to sdd (with dd) and then adding sdd as the missing drive help? linux software-raid raid-5 bad-sectors mdadm share|improve this question edited Feb 9 '12 at 9:28 asked Feb 8 '12 at 23:29 siebz0r 31619 How many bad sectors are there? If there are only a few, then fix them with hdparm. If there are many, then toss the drive and restore from backup. –psusi Feb 9 '12 at 2:55 Like any good administrator I don't have a backup. I assumed raid 5 would provide enough redundancy. I don't know how many bad sectors there are but it looks like it's quite random. I'm going to replace the sata cable first, then try again. –siebz0r Feb 9 '12 at 6:50 3 RAID5 is not a substitute for backup, they serve
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