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    SubjectRe: Blockbusting news, this is important (Re: Why are bad disk sectors numbered strangely, and what happens to them?)
    Quote from "Norman Diamond" <>:
    > Now, maybe there is a technique to force it anyway. When a partition is
    > newly created and is being formatted with the intention of writing data a
    > few minutes later, do writes that "should" have a better chance of being
    > detected. The way to start this is to simply write every block, but this is
    > obviously insufficient because my block did get written shortly after the
    > partition was formatted and that write didn't cause the block to be
    > reallocated. So in addition to simply writing every block, also read every
    > block. For each read that fails, proceed to do another write which "should"
    > force reallocation.

    I am just imagning how many Flash devices will be worn out
    unnecessarily by any filesystem utility that does this transparently
    to the user :-(.

    > Russell King replied to me:
    > > > When a drive tries to read a block, if it detects errors, it retries up
    > > > to 255 times. If a retry succeeds then the block gets reallocated. IF
    > >
    > > This is perfectly reasonable. If the drive can't recover your old data
    > > to reallocate it to a new block, then leaving the error present until you
    > > write new data to that bad block is the correct thing to do.

    I 99% agree with that. The 1% where I don't is that there may be
    situations where there is no interest in doing any data recovery from
    the drive, (you have backups, it is part of a RAID array, or storing
    temporary data that can be re-generated whenever necessary), and also,
    any read errors that occur during a S.M.A.R.T. read test should result
    in a re-mapping of the block.

    > > Think about what would happen if it did get reallocated. What data would
    > > the drive return when requested to read the bad block?
    > Why does it matter? The drive already reported a read failure. Maybe Linux
    > programs aren't all smart enough to inform the user when a read operation
    > results in an I/O error, but drivers could be smarter. I think there's
    > probably a bit of room in an inode to add a flag saying that the file has
    > been detected to be partially unreadable. Sorry for the digression.
    > Anyway, it is 100% true that the data in that block are gone. The block
    > should be reallocated and the new physical block can either be zeroed or
    > randomized or anything, and that's what subsequent reads will get until the
    > block gets written again.

    100% agreed.

    > > If the error persists during a write to the bad block, then yes, I'd
    > > expect it to be reallocated at that point - but only because the drive has
    > > the correct data for that block available.
    > We agree in our moral expectations and our technical analysis that correct
    > data will be available at that time. But if your word "expect" means you
    > have confidence that the drive will perform correctly, I do not share your
    > confidence (I think it is possible but highly unlikely that the drive did
    > its job correctly during the previous write).

    If the drive is not doing it's job properly DRIVE -> BIN.

    > > Your description of the way Toshibas drive works seems perfectly sane.

    I disagree - we haven't confirmed what happens in the error-on-write
    situation. If it does indeed always remap the block, then I'd agree
    that that aspect was perfectly sane.

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      Last update: 2005-03-22 13:58    [W:0.023 / U:36.644 seconds]
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