[Borgbackup] Question on "borg mount" performance

[Thomas Waldmann]

> 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?

Well, it is expected that FUSE mount is slower than extract.

You didn't write how slow it was so that we could directly compare.

Also the operations you did were slightly different:

a) your ran sha1sum directly on the file in the fuse mount - that might 
behave differently than copying the file from the fuse mount to 
somewhere else with cp depending on how many and how big read calls 
sha1sum does.

The FUSE mount also needs to do some preprocessing when you first enter 
a "archive directory" so it can know what file names it shall show you 
there.

It also does some caching to avoid having to get same chunks multiple 
times from the repo

b) extract doesn't do most of that

In general, if you know that you will deal with a huge amount of data 
(like a full extract, like extracting gigabytes), borg extract is more 
efficient.

> In any case, Borg is wonderfully documented, very complete in the
> features I need, and is written in Python. What could be better?

:)

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