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    SubjectBackups done right (was [ANNOUNCE] Ext3 vs Reiserfs benchmarks)

    It's really quite simple in theory to do proper backups. But you need
    to have application support to make it work in most cases. It would
    flow like this:

    1. lock application(s), flush any outstanding transactions.
    2. lock filesystems, flush any outstanding transactions.

    3a. lock mirrored volume, flush any outstanding transactions, break
    mirror.
    --or--
    3b. snapshot filesystem to another volume.

    4. unlock volume

    5. unlock filesystem

    6. unlock application(s).

    7. do backup against quiescent volume/filesystem.

    In reality, people didn't lock filesystems (remount R/O) unless they
    had too (ClearCase, Oracle, any DBMS, etc are the exceptions), since
    the time hit was too much. The chances of getting a bad backup on
    user home directories or mail spools wasn't worth the extra cost to be
    sure to get a clean backup. For the exceptions, that's why god made
    backup windows and such. These days, those windows are miniscule, so
    the seven steps outlined above are what needs to happen these days for
    a trully reliable backup of important data.

    John
    John Stoffel - Senior Unix Systems Administrator - Lucent Technologies
    stoffel@lucent.com - http://www.lucent.com - 978-399-0479



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