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.
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