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Five key questions about dump (continued)

Question 4
Do we really have to dismount the filesystem to get a consistent dump?
A: No.

There is a high likelihood that dumps of an idle, mounted filesystem will be fine. The more active the filesystem, the higher the risk that corrupt files will be dumped. The risk that files are corrupt is about the same for a utility that accesses files using the filesystem.

Question 5
Will we learn (after it's too late) that our dump of an essentially idle mounted filesystem is corrupt?
A: No.

It's possible that individual files in that dump are corrupt, but highly unlikely that the entire dump is corrupt. Since dump backs up data inode by inode, this is similar to backing up through the filesystem file by file.


Pass III
This is when real disk data starts to get dumped. During Pass III, dump writes only those directories that contain files that have been marked for backup. As in the Pre-Pass III phase, during Pass III, dump logically writes data something like this:

    Header (TS_INODE)
    Disk blocks (directory block[s])

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    Header (TS_ADDR)
    Disk blocks (more directory block[s])
    .
    .
    .
    Header (TS_ADDR)
    Disk blocks (more directory block[s])
    Repeat the previous four steps for each directory in the list of directory inodes to back up.

This was first published in August 2007

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