[lkml]   [1998]   [Dec]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: scary ext2 filesystem question
    > Really, I don't know what to add to this sentence.  Without
    > implementing partially ordered writes, this is a problem. Now, even
    > the author admits that this is "unlikely" to happen, and practical
    > experience says that it is at best extremely rare. Still, nothing
    > that the author said appears to be FUD or incorrect from what I know.

    Bang head on wall time. You need more than partially ordered writes to
    solve what you describe. Consider adding a 4K block to a file. You must

    The inode - new size, block count
    The indirect block (maybe blocks) with the block number
    The data block.

    Now you can order those however you like as strictly as you like I can
    still turn the power off at any point.

    Ext2fs (generally)
    update data block
    update inode
    update indirect block

    So potentially the data update is lost on a power off because the inode
    or indirect block isnt written.

    BSD (strict)
    update inode
    update indirect block
    update data block

    And if I turn the power off your file is 4K larger, consistent with its
    meta-data and containing 4K of unspecified random previous data - eg a previous
    copy of the shadow password file, a private note to your girlfriend whatever..

    You can pick any order of update you like, you still lose. Only a transaction
    based file system where you atomically write a transaction, then commit it
    is capable of resolving the situation.

    Anyone who can't grasp such basic facts shouldnt be writing books on file


    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    Please read the FAQ at

     \ /
      Last update: 2005-03-22 13:46    [W:0.022 / U:9.288 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site