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Hi guys

As far as I understood, the rsnapshot utility creates hard links when a
file did not change.
This means a great improvement is used disk space.

However, if I add one byte to a really big file, the file is considered
changed, and a complete copy will be made (?).

Would it be possible to do this on inode-level, so that only diffs *in*
files would make it into the snapshot?
I have seen this functionality in NetApp boxes, but I remember a Linux
Expo in Amsterdam a few years ago where such functionality was proposed
for the linux kernel. Anybody heard of this lately?

Anyway, thanks for the excellent tool,


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Dick Visser wrote:

As far as I understood, the rsnapshot utility creates hard links when a
file did not change.
This means a great improvement is used disk space.

However, if I add one byte to a really big file, the file is considered
changed, and a complete copy will be made (?).

Would it be possible to do this on inode-level, so that only diffs *in*
files would make it into the snapshot?

Do you mean blocks, and not inodes?

My understanding is that this would require first writing a filesystem,
and may also require writing an OS, because any block can, under most
(all?) Unixy filesystems, only belong to one file. Of course that file
can be pointed at by multiple directory entries. To have only the
differences stored, you would need to have two files sharing most of
their blocks.

This defnitly won't work on any of the most common Unixy filesystems -
fsck will throw a screaming fit next time you reboot. It may not fit
particularly well with the Unix Way - there are probably some pretty
deeply embedded assumptions about how filesystems are structured.

Incidentally, no-one commented on my mutterings a week or so ago about
doing deletes in the background. Am I to take it that people don't
think this is a stupid idea?

--
David Cantrell | Official London Perl Mongers Bad Influence

One person can change the world, but most of the time they shouldn't
-- Marge Simpson


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Hi David,

I think the deletes in the background are a great idea. Unfortunately
I've been very busy lately and haven't had as much time as I would like
to spend on rsnapshot.

If anyone is interested in writing this, I would certainly consider
including it in the main source tree.

Any dissenting opinions? The only drawback I could see is that it could
require more disk space. Perhaps it could be (yet another) option?

Thanks for the input!
-Nathan

David Cantrell wrote:

Incidentally, no-one commented on my mutterings a week or so ago about
doing deletes in the background. Am I to take it that people don't
think this is a stupid idea?




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Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
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