Single Instance Storage

Fraser Campbell fraser-eicrhRFjby5dCsDujFhwbypxlwaOVQ5f at
Wed Nov 16 13:47:55 UTC 2005

Dave Stubbs wrote:

> M$ SIS is a filter and a service that runs on top of the NTFS
> filesystem.  It allows you to copy many redundant copies of the same
> stuff onto a drive, and then during the night the "groveler" service
> walks the filesystem and finds any duplicate files, moving them to a SIS
> repository and replacing them in the user directory with something like
> a hard link.  It is different than the Posix concept of a link though -
> if you go and modify one of these multiple copies of the same file, it
> doesn't change all the others.  Instead it detaches the modified copy
> from the Single Instance Store, and makes it unique.

I believe the Linux vservers project does this:

* each virtual server is basically a chroot
* files in the chroot are hard links to a pristine filesystem
* as a virtual server modifies it's files the hard links are "broken"
   and new file is created
* admin has tools to consolidate differences over time and move common
   files back to hard links

If that's what you're after perhaps you should look at

Outside of the virtual machine world I think that unionfs and mapfs 
might do what you want.

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