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On Tue, Dec 23, 2014 at 4:08 PM, Holger Hoffstätte |
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<holger.hoffstaette@××××××××××.com> wrote: |
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> On Tue, 23 Dec 2014 21:54:00 +0100, Stefan G. Weichinger wrote: |
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> |
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>> In the other direction: what protects against these errors you mention? |
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> |
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> ceph scrub :) |
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> |
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Are you sure about that? I was under the impression that it just |
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checked that everything was retrievable. I'm not sure if it compares |
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all the copies of everything to make sure that they match, and if they |
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don't match I don't think that it has any way to know which one is |
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right. I believe an algorithm just picks one as the official version, |
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and it may or may not be identical to the one that was originally |
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stored. |
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If the data is on btrfs then it is protected from silent corruption |
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since the filesystem will give an error when that node tries to read a |
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file, and presumably the cluster will find another copy elsewhere. On |
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the other hand if the file were logically overwritten in some way |
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above the btrfs layer then btrfs won't complain and the cluster won't |
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realize the file has been corrupted. |
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If I'm wrong on this by all means point me to the truth. From |
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everything I read though I don't think that ceph maintains a list of |
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checksums on all the data that is stored while it is at rest. |
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-- |
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Rich |
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