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Thread: bit error = lost file, reduce BER how?

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  1. #19
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    Quote Originally Posted by m^2 View Post
    So RAID controller just flips a bit on one drive, not necessarily the correct one? Therefore I don't see any significant advantage of RAID 6 over RAID 5 here.

    What happens if there's error on the drive that internal ECC can't correct? Drive returns error message and RAID can use another drive to get the data, right?

    BTW do you know anything about chance of getting bit corruption in case of having RAID+ECC mem?
    I mean (undetected) error on HDD / in memory / cables etc.?
    I guess that if industry doesn't care, it's a very minor thing, but it would still be good to know the problem.
    I'll try:

    RAID 5, you have to tell it which bit to favor, parity or original data. This means no real protection other than preventing corrupt volumes.

    RAID 6, there are 3 bits and the odds of 2 bits being bad are small, therefore when the bad data is fixed, odds are good it really was the bad data and you are doing the equivalent of a coin toss.

    As far as RAM bit errors, the original Corsair rule I recall is: 1 bit error occurs in 256MB of ram every month.
    4GB = 15 bit errors/month
    8GB = 31 bit errors/month
    16GB = 62 bit errors/month
    32GB = 125 bit errors/month

    However, other more recent sources maintain 1 bit error per gigabyte per month, so that cuts those numbers by a factor of 4, i.e.:
    4GB = 4 bit errors/month
    8GB = 8 bit errors/month
    16GB = 15 bit errors/month
    32GB = 31 bit errors/month

    Which is more correct? My guess is that it's somewhere in between, governed by the quality of the RAM, amount of overclock beyond stated specs, the luck of the draw, and a host of other issues.


    Anyone with more up to date or correct info please feel free to correct me.
    Last edited by Speederlander; 12-29-2008 at 09:28 AM.
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