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    SubjectRe: Building Big Ass Linux Machine, what are the limits?
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    | As far as I know it uses copy-on-write.. this means that you only have one
    | copy of the data - the most recent. Snapshots are only the bytes that
    | are different... applied (as a patch would be) to the most recent version.

    it is copy-on-write, but it is not a patch, it's a completely different block.
    basically, assume you have a file using blocks 4, 5, and 6. That is in the
    current filesystem (aka: consistency checkpoint.)

    if you don't change the file, and then create a new snapshot (#1), the blocks
    are the same, and the inode in snapshot 1 points to the same data blocks (4,
    5, and 6.)

    now, say you append to the file. snapshot 1 still points to (4,5,6), and the
    current filesystem will point to (4,5,7), where block 7 is copied data from
    block 6, plus the appendage.

    snapshots are a read-only view of the file system at the time of the snapshot.

    for a graphical interpretation, see http://www.netapp.com/technology/level3/300
    2.html, page 11.

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