[Bug-ddrescue] Sparse and preallocate questions/feature idea

[Zeniff Martineau]

Does ddrescue estimate how sparse an output file will be when using
--preallocate?

If not, I'd like to suggest it as an option to do so and output the
expected output file size.

Maybe it can do so without even trying to write an image, like a dry-run?


I have two 1 TB HDDs, one which probably was used a lot, the other
just a few times. I assume more usage over time leads to less chance
of a smaller sparse output file because of empty space not all being
zeroes. Is this right?

I'm basically just curious if I can fit both entire HDD image files
onto one bigger destination, or if I might have to copy the source
partitions individually and place them in spare space on smaller
destination drives, or maybe just compress the actual files via
mounting the partitions and tar/compressing instead of using ddrescue
on the HDDs at all?

I'm also curious about how it could be done. I think find(1) utility
can look at sparseness of files, but how about the free space on a
drive?

Or, is there some CLI or GUI program which can give me an idea of how
much actual unused (all zeroes) room there is (maybe visually like the
Windows defrag utility used to show)? I mean on a large scale, since
I'd like to see as much of the drive as possible at the same time;
kind of like a disk usage analyser, but instead for all space.

I guess it all boils down to me trying to figure out how best to use
the HDDs I have without buying more as long as possible, and therefore
putting data (much of which is from older/smaller HDDs via ddrescue)
onto whichever drives it'll fit best. :P

Sorry for the curious ramblings. I hope that made sense. Have a great day~! ^^