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And so we enter day seven of King's College London major IT outage

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Why RAID 6 stops working in 2019

WTF am I reading?

The problem with RAID 5 is that disk drives have read errors. SATA drives are commonly specified with an unrecoverable read error rate (URE) of 10^14. Which means that once every 200,000,000 sectors, the disk will not be able to read a sector.

So... are there any that are lower? Hint. Not SCSI, which are the same drives with a changed controller.

2 hundred million sectors is about 12 terabytes. When a drive fails in a 7 drive, 2 TB SATA disk RAID 5, you’ll have 6 remaining 2 TB drives. As the RAID controller is reconstructing the data it is very likely it will see an URE. At that point the RAID reconstruction stops.

I seriously hope that RAID reconstruction does NOT stop (aka. throwing the baby out with the acid bath), as there is a very nonzero probability that the smoked sector is not even being used.

With one exception: Western Digital's Caviar Green, model WD20EADS, is spec'd at 10^15, unlike Seagate's 2 TB ST32000542AS or Hitachi's Deskstar 7K2000


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