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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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Grant Edwards grant.b.edwards Yow! ... he dominates the |
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at DECADENT SUBWAY SCENE. |
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gmail.com |