Correct, resumable, large-file flags

[Mark Raynsford]

Hello.

I'm a long-time rsync user, but I've encountered a case today and I
just can't seem to get rsync to do the right thing.

I want to mirror a directory A on server www1.example.com to a
directory B on www2.example.com. The directory A contains very
large but essentially read-only files. A server process on
www1.example.com periodically creates new large files and deletes old
ones. I want to synchronize the directories roughly every ten minutes.
It's important that a file in B only becomes "visible" (that is, has
the same name as a file in A) when the two files contain the exact
same content. Files that no longer exist in A should be deleted from B.

An initial pass:

  www1$ rsync -avz --delete-after /A/ www2.example.com:/B/

This works, but the transfers are not resumable for some reason. If I
^C the rsync process and then run it again, I see partial files left in
B, and rsync ignores these the next time I run the command.

I've seen this:
https://unix.stackexchange.com/questions/48298/can-rsync-resume-after-being-interrupted

But, quite frankly, I feel like I've tried every combination of flags
and can't get the behaviour I'm looking for. Either rsync copies the
files in-place (violating the invariant that a file in B should should
not be visible by the name it had in A before the contents match), or
it places partial files in the same directory (or in a
separate .rsync-partial directory) but then ignores them next time the
transfer runs.

Can someone spell it out for me? Which flags do I need?

-- 
Mark Raynsford | http://www.io7m.com

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