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Am 08.01.2013 20:53, schrieb Grant Edwards: |
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> On 2013-01-08, Pandu Poluan <pandu@××××××.info> wrote: |
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>> On Jan 8, 2013 11:20 PM, "Florian Philipp" <lists@×××××××××××.net> wrote: |
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>>> |
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>> |
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>> -- snip -- |
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>> |
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>>> |
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>>> Hmm, good idea, albeit similar to the `md5sum -c`. Either tool leaves |
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>>> you with the problem of distinguishing between legitimate changes (i.e. |
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>>> a user wrote to the file) and decay. |
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>>> |
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>>> When you have completely static content, md5sum, rsync and friends are |
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>>> sufficient. But if you have content that changes from time to time, the |
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>>> number of false-positives would be too high. In this case, I think you |
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>>> could easily distinguish by comparing both file content and time stamps. |
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>>> |
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>>> Now, that of course introduces the problem that decay could occur in the |
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>>> same time frame as a legitimate change, thus masking the decay. To |
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>>> reduce this risk, you have to reduce the checking interval. |
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>>> |
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>>> Regards, |
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>>> Florian Philipp |
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>> |
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>> IMO, we're all barking up the wrong tree here... |
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>> |
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>> Before a file's content can change without user involvement, bit rot must |
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>> first get through the checksum (CRC?) of the hard disk itself. There will |
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>> be no 'gradual degradation of data', just 'catastrophic data loss'. |
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> |
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> When a hard drive starts to fail, you don't unknowingly get back |
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> "rotten" data with some bits flipped. You get either a "seek error" |
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> or "read error", and no data at all. IIRC, the same is true for |
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> attempts to read a failing CD. |
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> |
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> However, if you've got failing RAM that doesn't have hardware ECC, |
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> that often appears as corrupted data in files. If a bit gets |
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> erroneously flippped in a RAM page that's being used to cache file |
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> data, and that page is marked as dirty, then the erroneous bits will |
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> get written back to disk just like the rest of them. |
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> |
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|
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Related: The guys in [1] observed md5sums of data and noticed all kinds |
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of issues: bit rot, temporary controller issues and so on. |
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|
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[1] Schwarz et.al: Disk Failure Investigations at the Internet Archive |
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http://www.hpl.hp.com/personal/Mary_Baker/publications/wip.pdf |
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|
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Regards, |
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Florian Philipp |
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