Re: [rdiff-backup-users] Ignoring resource forks

[Simon Hobson]

Matthew Flaschen wrote:

> Why would the data file always be different if as you said, it excludes
> both the resource fork and metadata?

I think (and again, it's quite some time since I looked into this so 
I could be completely wrong !) that's it's down to a rather brain 
dead implementation ! I thought it was something to do with the 
receiving end working with "file" as a complete entity which of 
course doesn't match "file" (data fork only) plus "._file" offered by 
the sender. Thus the file gets sent again (as two files which get 
re-assembled).

Actually, I've been doing a bit of searching, and found a few 
references. Some are a bit old, but I get the impression that Apple 
might not be applying full priority to fixed the issues. This is of 
course getting somewhat off-topic for this list - but it is "sort of 
related" for people doing backups on OS X. Some of the links mention 
extended attributes, and I can confirm that in 10.5, extended 
attributes are definitely in use* - but I don't know how widespread 
they are.

It was even more interesting to read in one of these references that 
HFP+ actually support arbitrary forks, not just resource and data. In 
that respect it has something in common with NTFS which supports 
arbitrary threads within a file - conceptually very similar.**

http://www.bombich.com/mactips/rsync.html
"I strongly encourage you to use rsync 3.0.5 or greater for Tiger and 
Leopard. The version of rsync that Apple ships with Tiger and Leopard 
does not perform as well as rsync 3.0.5, consumes more memory 
(especially for transfers of many files), and will copy unmodified 
resource forks every single time."

http://www.n8gray.org/blog/2007/04/27/introducing-backup-bouncer/

http://blog.plasticsfuture.org/2006/03/05/the-state-of-backup-and-cloning-tools-under-mac-os-x/

http://www.oreillynet.com/cs/user/view/cs_msg/66135

http://mjtsai.com/blog/2006/01/16/fixing-rsync-on-tiger/


* Ones I know about are some core system files, and Time Machine 
archives are tied to the MAC address of your ethernet port (so you 
need to change the MAC in the extended attribute if you have your 
logic board replaced if you want your TM archive to be recognised - 
guess how I found that out !)

** Something I gleaned from a talk given by Jeremy Allison of the 
Samba project. As Microsoft do not have any OS still in support that 
doesn't support this feature, it could suddenly get used at any time 
and the Samba team need to consider how to handle it.

--
Simon Hobson

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