Re: Expected behavior of bad sectors on one drive in a RAID1

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2015-10-21 07:51, Austin S Hemmelgarn wrote:
> On 2015-10-20 15:59, Austin S Hemmelgarn wrote:
>> On 2015-10-20 15:20, Duncan wrote:
>>> Yes, there's some small but not infinitesimal chance the checksum may be
>>> wrong, but if there's two copies of the data and the checksum on one is
>>> wrong while the checksum on the other verifies... yes, there's still
>>> that
>>> small chance that the one that verifies is wrong too, but that it's any
>>> worse than the one that does not verify?  /That's/ getting close to
>>> infinitesimal, or at least close enough for the purposes of a mailing-
>>> list claim without links to supporting evidence by someone who has
>>> already characterized it as not mathematically rigorous... and for me,
>>> personally.  I'm not spending any serious time thinking about getting
>>> hit
>>> by lightening, either, tho by the same token I don't go out flying kites
>>> or waving long metal rods around in lightning storms, either.
>> With a 32-bit checksum and a 4k block (the math is easier with smaller
>> numbers), that's 4128 bits, which means that a random single bit error
>> will have a approximately 0.24% chance of occurring in a given bit,
>> which translates to an approximately 7.75% chance that it will occur in
>> one of the checksum bits.  For a 16k block it's smaller of course
>> (around 1.8% I think, but that's just a guess), but it's still
>> sufficiently statistically likely that it should be considered.
> As mentioned in my other reply to this, I did the math wrong (bit of a
> difference between kilobit and kilobyte)
And I realize of course right after sending this that my other reply 
didn't get through because GMail refuses to send mail in plain text, no 
matter how hard I beat it over the head...



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