[RndTbl] rsync with multi-direction delete.

[Montana Quiring]

OK.
Thanks everyone for your input.
I don't feel quite so bad for not being able to figure this out in a
timely fashion. :)

A couple things to note are:
-When I delete something on either master I would always want it gone from both.
-I would only be modifying files on the master on the server
-i would never be adding files to the master on the USB device, I
would only be deleting files.

I guess I can handle having one master. I'll just always delete the
files from the server when I want to get rid of them. Not a big deal.

I'll look into Union too.

-Montana

On 9/17/07, Sean Cody <sean at tinfoilhat.ca> wrote:
> Multi-master with rsync is well... there be dragons.
> At least this is a very easy way to drive yourself insane.
>
> I speak from experience here; for another PoV ask SW the pains this
> can cause, especially once the data set gets huge and the file system
> comes really busy.
> There is an 'methodology' hack which can work quite well but it isn't
> a true multi-master... think of it as a segregated master and it
> won't work in this situation.
>
> I would really give up trying to make rsync do multi-master...
> seriously that way leads to madness and lost data (without decent
> locking there will be race conditions and difference/delta timing/
> transaction problems).  I would suggest re-thinking your work flow to
> move towards a single master solution and just doing very periodic
> backups of the master (think revision control systems).  You could
> also try rsnapshot (check google) but that's shoe horning and still
> requires single master.
>
> On 17-Sep-07, at 3:17 PM, Adam Thompson wrote:
>
> > Montana Quiring wrote:
> >> What I want: when I delete a file or directory on either place it
> >> will
> >> remove it from the other.
> >> What it does now: If I delete a directory or file from the server it
> >> removes it from the USB device (ya!) but if I remove a file/directory
> >> from the USB device and perform an rsync it replaces the deleted
> >> file/directory.
> >>
> >> Here is the rsync command I'm using:
> >> rsync --delete --delete-excluded --recursive -uv
> >> quiringm at 192.168.1.102:/mnt/hdd/music/podcasts/ /Volumes/MEK/
> >> Podcasts/
> >>
> > As Bill already suggested, rsync might not be ideal for this
> > situation, as it assumes a single-master scenario; you're looking
> > for a multi-master architecture.
> >
> > There is one easy way to use rsync - but you have to know in
> > advance which location has the deleted files, and name that as the
> > source.  So when sync'ing from server to USB, use the command you
> > mention above, but when syncing from USB to server, reverse the
> > last two arguments.  You see immediately that you can only make
> > changes to one location OR the other in between syncs, as any
> > changes made in one location will always be undone by the other.
> >
> > In fact, true two-way synchronization in the manner you're talking
> > about is still a fairly hard problem in the generic case.  It's
> > fairly easy if you have some way of keeping a log of all activity
> > to both trees, you can compare timestamps to see whose actions need
> > to be replicated where, but without any a priori knowledge, how is
> > any tool supposed to know the difference between these two scenarios:
> >
> >    A.  You've added a directory (and some files) to system #1, that
> > don't appear on system #2 yet.
> >
> >    B.  You've deleted a directory (and some files) on system #2,
> > but they remain on system #1.
> >
> > To a sync tool comparing systems #1 and #2, those two scenarios are
> > indistinguishable.  And, so far as I know, there's no DWIM
> > extensions to rsync yet :-)
> >
> > One package that *might* be able to solve your problem with some
> > extra work on your part is XFile (http://www.idiom.com/~zilla/
> > xfiles.html).
> >
> > Good luck with this...
> >
> > -Adam
> >
> >
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>
> --
> Sean
>
>
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