Re: If your using large Sata drives in raid 5/6 ....

[John Robinson <john.robinson@anonymous.org.uk>]

On 05/02/2010 15:38, Bill Davidsen wrote:
> John Robinson wrote:
[...]
>> What sums I've done, on the basis of a 1 in 10^15 bit unrecoverable 
>> error rate, suggest you've a 1 in 63 chance of getting an 
>> uncorrectable error while reading the whole surface of their 2TB disc. 
>> Read the whole disc 44 times and you've a 50/50 chance of hitting an 
>> uncorrectable error.
>>
> Rethink that, virtually all errors happen during write, reading is 
> non-destructive, in terms of what's on the drive. So it's valid after 
> write or it isn't, but having been written correctly, other than 
> failures in the media (including mechanical parts) or electronics, the 
> chances of "going bad" are probably vanishingly small.

They're quite small, at 1 in 10^15 bits read. On 1GB discs, you probably 
could call it vanishingly small. But now with 1TB and larger discs, I 
wouldn't characterise it as vanishingly small. It's entirely on the 
basis of the given specs that I did my calculations.

Bear in mind that the operation of the disc is now deliberately designed 
to use ECC all the time. Have a look at the vast numbers you get from 
the SMART data for ECC errors corrected. I just checked a 160GB 
single-platter disc with 4500 power-on hours; it quotes 200,000,000 
hardware ECC errors recovered.

Cheers,

John.