Re: COW files

[Hans Reiser <reiser@namesys.com>]

Gregory Maxwell wrote:

>Any thought to making a file plugin that creates copy on write files?
>The operation would be something like a hardlink which is invisible to
>the user and broken as soon as either file is modified.
>
>Files could be COWed by a flag on the cp command (or really, perhaps
>that should be the default behavior) or with a utility (perhaps run as
>a periodic script to locate duplicates and COW them. This would
>greatly speed up the process of copying files.
>
>The behavior on break could be to duplicate the whole cowed file on
>the first right, or allow a COWed file to have alternate choices for
>blocks. Files would remain cowed until decowed, which would likely be
>bad for performance (due to fragmentation of alternate versions
>causing gaps in sequential scans), so the repacker could be taught to
>decow files that have too many alternate blocks.
>
>
>  
>
we are open to patches for this, and nobody is writing one....;-)