Is RAID 5 save for 4 hdd 3 TB each.

[mindaugas]

HI,

I red articles, that it could be unreadable sectors (URE) :

"
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?
"

http://www.zdnet.com/article/why-raid-6-stops-working-in-2019/

The second question is: is possible to run fixers or jobs to fix all bad unreadable sectors before 1 drive fails ?

Thanks for help,
Min.