[Borgbackup] Question on "borg mount" performance

[Antoine Beaupré]

On 2016-04-22 09:14:35, Terry Phelps wrote:
> First: I just discovered Borg a few days ago. I have been searching for
> some sort of usable de-deduplicating backup program. I am in the early
> stages of using Borg to backup VM disk images. Some of these images have
> lots in common with other disk images, so I have a lot to gain by using
> some form of de-deduplication.
>
> I was just now going to do some verification of of the backups, by
> comparing the SHA1 sum of the original VM disk image ( a clone, really, so
> it doesn't chnage) to the SHA1 sum of the backup. I first did a "borg
> mount", and did "sha1sum /mnt/.../disk.image" directly from the FUSE mount.
> This was horribly slow. I then did a "borg extract" of that same disk
> image, and that was much, much faster.
>
> Is this what you expected? Is the FUSE mount method known to be very slow
> when reading, say, a 10-GB file, as compared to extracting that same file?

It seems to me we should have a `diff` command that would remove the
need to extract big files or use the slower FUSE interface (if only
because that needs to build a directory tree).

The diff command is currently limited to diffing between archives, so
right now you could create an archive and diff, but that seems like a
huge overhead as well.

I have opened a feature request about this:

https://github.com/borgbackup/borg/issues/963

a.

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