The Real (and Virtual) Adventures of Nathan the IT Guy

Feb 23 2010   3:07AM GMT

Why RAID 6 stops working in 2019



Posted by: Nathan Simon
Tags:
hdd failure
RADI 5
RAID 6
unrecoverable read error rate
URE
zdnet

To think that technology has come so far in the last 10 years, and now RAID arrays are becoming a risk! This is information everyone should read…

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.

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.

Here’s the math:
1 – 1 /(2.4 x 10^10)) ^ (2.3 x 10^10) = 0.3835

You have a 62% chance of data loss due to an uncorrectable read error on a 7 drive RAID with one failed disk, assuming a 10^14 read error rate and ~23 billion sectors in 12 TB. Feeling lucky?

Read the rest of the article over at ZDNet.

-NS

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