[mythtv-users] 2 TB Hard Drive Recommendations

[Simon Hobson]

Jean-Yves Avenard wrote:

>so two drives out of 6 dying in 18 months, so close to each other
>isn't that great.

That's one of the problems where the idea of RAID breaks down. You 
buy a set of disks (same make and model, possibly even from the same 
manufacturing batch), stuff them in an enclosure, and run them for 
the same power on hours, doing the same usage profile - ie they are 
run under near identical conditions. That means the failures are 
liable to be less distributed temporally than you might be thinking.

So you've massively increased the chance of two (or more) 
simultaneous failures.

I saw that in one of our Unix servers at my last job. A drive failed, 
and it took our maintainers a while to get a replacement because they 
struggled to understand that they can't supply any old "9GB drive" 
and it must be at least the same number of blocks as the smallest in 
the array. By the time it did get replaced, two more were showing an 
increasing error count and I think we replaced 3 in an array of 4 ! 
For that reason, I've always setup my arrays to use a bit less than 
the full disk to allow for a slightly smaller drive as a replacement.

So I think there is an argument (if possible) to at least spread your 
purchases and build the array over several months - if you use all 
the same drive, that should at least give you a chance of them coming 
from different batches and reduce the chance of a common defect.

-- 
Simon Hobson

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