On Sat, 4 Jul 2015 10:10:46 +0200 (CEST)
Mikael Abrahamsson [off-list ref] wrote:

quoted

Are these 3TB Seagate Barracudas? (Same as mine). You DO NOT want to be
running raid 5 or 6 on these things !!!! They're desktop drives not
meant for raid.

Not only that, but they're known to have en extremely high failure rate:

https://www.backblaze.com/blog/3tb-hard-drive-failure/

"As of March 31, 2015, 1,423 of the 4,829 deployed Seagate 3TB drives had 
failed, that’s 29.5% of the drives."

And the cause is... http://habrahabr.ru/post/251941/
(Use Google Translate if you have to, or just look at the pictures)

An unfortunate hardware design flaw, leading to dust from the outside
eventually getting into the drive's platter area, and then starting to chip
away ferromagnetic particles from the actual platters.

-- 
With respect,
Roman