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On Fri, Sep 18, 2015 at 2:19 PM, Mick <michaelkintzios@×××××.com> wrote: |
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> On Friday 18 Sep 2015 19:15:50 Rich Freeman wrote: |
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>> On Fri, Sep 18, 2015 at 1:56 PM, Mick <michaelkintzios@×××××.com> wrote: |
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>> > On Friday 18 Sep 2015 17:16:54 Marc Joliet wrote: |
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>> >> On Friday 18 September 2015 10:31:01 Mick wrote: |
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>> >> >A couple of months ago the akonadi DB went sideways and kmail played up |
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>> >> >as a result. Again I was suspicious of btrfs, but neither the logs |
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>> >> >nor fsck showed up anything. |
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>> >> |
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>> >> I take it "btrfs scrub" didn't turn up anything, or is that what you |
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>> >> meant by fsck? |
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>> > |
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>> > Am I supposed to run scrub with I do not have a RAID running? I thought |
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>> > scrub was meant for comparing checksums between mirrored fs - have I got |
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>> > this wrong? |
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>> |
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>> You can actually run scrub on a non-raid btrfs setup. Btrfs will |
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>> report any errors that it detects (using the checksumming in the |
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>> filesystem), but it would not be able to fix errors unless you have it |
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>> storing redundant data somewhere (even on non-raid it still stores |
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>> redundant metadata by default, and you can choose to do this with data |
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>> as well which protects against block-level failures but not disk-level |
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>> failures, obviously). |
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>> |
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>> However, you'd have gotten the same errors in dmesg just trying to |
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>> read the files - btrfs checks the checksum on all file read |
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>> operations. That is a big part of the value of both btrfs and zfs. |
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> |
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> Ah! V interesting ... can I run scrub with mounted partitions, or do I have |
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> to do it from a LiveCD? |
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|
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I didn't check, but I suspect you can only run scrub on a mounted |
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partition. I also suspect that fsck probably has an option to do |
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something equivalent offline. |
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|
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You do get the error-detection anyway just by reading files, and if |
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you just ran find on your filesystem and catted every file you have to |
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/dev/null that would actually accomplish the same thing as long as |
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you're not in a redundant mode (simply reading all the files doesn't |
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guarantee that all copies of each file are checked). |
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The main reason for doing a scrub is to detect latent issues, and if |
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you have redundancy that means you can auto-correct them today, rather |
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than discovering them a month from now when the drive containing the |
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only good copy fails. Even if you don't have redundancy maybe you |
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rotate your backups every 30 days and detecting the error might mean |
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having the ability to go back and restore a good copy of the file |
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before it is completely replaced with bad copies. |
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-- |
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Rich |
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