[ale] Copy-on-write file?

[Brian W. Neu]

have you looked at NILFS?

http://www.nilfs.org/en/


On 1/17/2010 9:11 AM, JK wrote:
> Hi everyone,
>
> ddrescue kicks a*s -- it imaged all but about 20MB of my 80GB failed
> HFS partition successfully.  I then made a copy of the image so as to
> have a backup in case I hosed the original (via fsck or simple
> dumbness on my part).  Making the backup took about 5 hours, which
> kinda sucked; and if I *do* need to revert to the backup image,
> copying for another 5 hours is not an appealing prospect.  What I'd
> really like is a way to tell the Linux kernel: "Please treat this
> file as copy-on-write -- if I write something to it, allocate a new
> on-disk block to hold the written data, splice that block into the
> file, and leave the original alone."  That way, going back to the
> clean image would merely be a matter of throwing away the COW blocks,
> instead of waiting another 5 hours to copy my backup image.
>
> Surely such magic is already available somehow? I know there are some
> distros that implement "writable" CDROM filesystems in a similar
> way, by using specialized COW filesystems, but that isn't exactly
> what I want.  I want to either
> (a) set up COW for a single file on an EXT3 FS, or else
> (b) mount the disk image as an HFS+ volume, in such a way that writes
> will not alter the image itself.
>
> (BTW I found the ext3cow FS, which would work, but something less
> intrusive would be awfully nice.)
>
> TIA,
>
> -- JK
>
>
>