[mythtv-users] Hard Drive reliability esp. RAID issues

John Drescher drescherjm at gmail.com
Mon Mar 8 17:20:13 UTC 2010


>> I would say from experience that this is very unlikely that a second
>> drive will fail in the 8 hours it takes to rebuild a 6TB array. And
>> even if it did with linux software raid you could recover. With HW
>> raid you will probably need specialized software to force the array to
>> except drives that are marked bad.
> The problem is not that a second drive will fail.  The problem is, statistical
> speaking, that 1 bit of 10 TB is unreadable, the so called UER (uncorrectable
> error rate).
> See this document from 2005 http://arxiv.org/pdf/cs/0701166
>
> This means that if you have to rebuild a 10 TB raid, you have to read 10 TB to
> calculate the parity bit.  But 1 bit will not be readable, so bye bye raid 5.
>
> What if you have a 10 TB disk?  Then a simple mirror will not be enough
> because you can never read the disk without missing 1 bit.
>

I have over 30TB of software raid 5/6 and I have never had a single
unreadable bit bringing down a raid.


John


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