Optimizations and other questions for rsync

Farid Shenassa FShenassa at usaninc.com
Wed Oct 16 21:00:01 EST 2002

Hello Everyone,

I've just started using rsync to copy files from  Windows NT RCS library to
Stratus VOS (Posix like fauilt tolerant Mini system) as a shadow.    I would
also like to setup rsync to copy log or other process output files from VOS
to an NT system.   Some questions if anyone here can help:

1. is there any computational or disk IO difference between the rsync client
and server (the one that does just the checksum on the block, vs the one
that does rolling checksum).  Given that I do not have as much cpu on the
VOS machine, I would like the more expensive side to run on the Windows
system.  So I need to figure out who should run the daemon and who should
push vs. pull.

2. is there a way for rsync to cache previous calculations on checksum, or
be told that a particular file of  regex filename starname is always
appended to, so it does not read the entire file?  Basically I have
processes that constantly append to ann output file on VOS.  I would like to
mirror these onto the NT machine.     However, I do not want to have rsync
every few minutes read the entire file.   Choices I see are:
	a. tell rsync that the file is append mode, so it just picks up from
the last block size on the other machine and goes forward
	b. rsync is smart enough not to do this on its own
	c. rsync can store cached checksum information
	d. there is another option that tells rsync to do this that I
	e. there is an option to tell rsync to basically continue to read
the file every X interval after it gets to the end without exiting.

3. expanding on option 2e.  One possibility would be to run rsync for each
file being synced and telling it to just sync to the end, then stay in
memory, and look for file changes or try to read more blocks at the end
(assuming another process is writing to it), and sync those new blocks.
This would keep rsync from stopping and having to restart from the
beginning.  It may however, cause memory issues for large files if it keeps
the whole checksum in memory?

Any ideas or other ways to get around this?   Again, question 2/3 are for
basically syncing open log files to another machine efficiently.  There may
be another tool out there for this that I'm not aware of, if so, please
enlighten me so I can stay away.

Thanks in advance for any help.
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