[Dirvish] dirvish: no incremental on Mac OS 10.4

Bernd Haug haug at berndhaug.net
Wed Oct 25 14:36:17 PDT 2006


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Keith Lofstrom wrote:
> Macs use a different kind of file system ( "HFS" ) with "data" and
> "resource" forks for each file.

I know, and I wanted to state something to this effect in the mail,
but forgot. Thanks for reminding me.

> These do not have unix kinds of
> permissions and mod dates

Well, AFAIK they do. Obviously not the same on-disk format bit by
bit, but
- --------
$ ls -li file
1507 -rw-rw-rw-   1 me  me  476109 Sep  2  2004 file
$ ln file file2
$ ls -li file2
1507 -rw-rw-rw-   2 me  me  476109 Sep  2  2004 file2
$
- --------
looks pretty unixish to me.

Also, and that's just IMO, Macs these days seem to have a lot more
continuation with Unix than old Macs under the hood; the UI is
pretty much tacked on there.

In fact, I got a Mac because I wanted a really mobile-capable Unix;
the whole graphical stuff was more of an add-on to me. I still
mostly use Thunderbird and xterm; the same as before with Linux.

> , and don't keep their associations when
> transferred to different file systems.

What kind of associations do you mean? Date and contents stay the
same; and inode isn't the same (or rather, may or may not be the
same) on any Unix.

Is there something obvious I missed on a layer that's important to
dirvish?

> As a result, rsync, which
> is the core of dirvish, gets confused.  Apple built their own 
> version of rsync to deal with this, but I doubt it would be properly
> interoperable for incremental backups unless there are Macs at 
> both ends.  While the resource fork is depreciated in current
> Mac applications, it has a strong legacy and will take a long time
> to go away.

I don't care so much about resource forks; I want the data to be
correct and in incremental backups; the Mac-specific Metadata isn't
important to me.

By the way, Macs (mostly!) seem to use alternative streams like
resource forks much the same way as Windows or new Unix FSs (ZFS
springs to mind):
They're there but nobody uses them for important stuff because they
break lots of tools.

BTW, to reiterate: There are Macs on both ends (basically, there is
only one end; local disk), and I've tried local transport too, which
breaks in the same way, only faster.

> Your best bet, if you are feeling ambitious, is to go to the rsync
> mailing list and look for "Tiger" or "10.4" and start following
> the threads.  I hope there is a solution, but nothing immediately
> springs to mind.  I hope you can come up with a solution, because
> I want to do network backups on my sister's computer and rsync
> and dirvish are the only practical way to move daily backups many
> miles.

Yeah, it's *very* broken. But if rsync wants to stay relevant, it
will have to get this right sooner or later, as more and more OSes
implement alternative data streams (which I'm not sure is a good
idea, but as a matter of fact, they do).

Anyway, I'm as sure as somebody who doesn't yet have a complete
picture about what's going on can be that the problem is not the
usual rsync-on-Mac breakage.

In any case, thanks for your reply!

Yours, Bernd
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