OT: Tip - Useful system utility

[Fairlight]

I know we have a lot of rsync fans here, so I thought I'd share a bit of
good evolutionary news.

I basically have several systems that can be live or failover, and which
reverse roles.  Some of the files are fP-related, some aren't.  All are
necessary for production.

I looked at a lot of alternatives, including the nightmare of complexity
and trouble that come with HA solutions like heartbeat + DRBD (which is so
poorly documented I could cry).  Everything seemed to be insufficient to
the task of keeping two systems "hot", or was painfully overcomplicated
with the potential for split-brain -anyway-, in addition to extra penalties
in relation to filesystem unavailability on a secondary node, etc.

In the end, my search led to Unison.  In short, Unison is much like rsync.
It uses the rsync protocol, and when needed or desirable, will use rsync
for higher efficiency in some tasks like large initial copies.

Where it really shines is in what it brings to the table beyond rsync:

* It's bidirectional, but controllable from one side.

* It has conflict detection built in, along the lines of VCS suites.

* It can actually do merges with external tools like emacs or diff3.  I'm
  using diff3.)  You can preview the differences prior to merge, and choose
  from a host of options...and even reject propogating a merge.

* It's about as fault tolerant as you could ask for, and has good
  diagnostics for automated alerts.

* GUI and text interfaces available in the same package.  (I'm only using
  text-based.)

If you love rsync, you should love this.  It lends itself to many purposes,
including road warrior laptop syncing...bidirectionally, simultaneously.
It's not full VCS for development, but brings strengths of VCS to your data
synchronisation to the degree necessary.

http://www.cis.upenn.edu/~bcpierce/unison/index.html

I'm rarely pleased enough with something enough to put it out there
unsolicited, but this is an excellent tool.

mark->
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