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With
the usual caveats of "Your Mileage May Vary", this may give you an idea of how
far you can push things and get away with it.
In
practice, I back up production MySQL databases when they are running. Not that
big a deal.
Some
notes on improving the odds (of getting away with it):
One
logical rsync is two rsyncs back-to-back.
The
first one to "do all the work"
The
second one to catch anything that changed during the first.
This
still leaves a window of expsure, but it is fairly small.
If the
rsync is over internet (or WAN) links,
a
local rsync to a staging area and the long slow rsync from something
"stable".
This
is with straight MyISAM tables. I would expect trouble from anything with
"transactional integrity".
With
MyISAM, things are simple enough so that even if you catch somehting in
mid-something, its actually pretty hard to trash the table. That's hard, not
impossible. Actually with staged backups, it's pretty well impossible to
actually do yourself in.
The only time I've gotten bit (that I'm aware
of) is the .MYD and the .MYI out of sync and adding a new record and getting bit
because the autoincrement record already existed. Actually more funny than
serious.
If you
have only the primary and one backup (just one backup seems a recipe for
disaster, anyway), you will need to stop the database and do the rsync. (And
what do you do when the primary fails DURING the rsync?)
Backing up from Windows, my guess is that you will have better luck doing
an smb mount and doing the rsync from something unixy to something unixy. With
windows, a file opened normally will have EVERYTHING ELSE locked out of doing
anything with that file. With things unixy, it is considered kosher to delete a
file while someone else is writing it, the standard sequence of an update is to
./configure; make; make install. Then to shut down the old running program and
bring up the new program. The smb mount and unix rsync will NOT overcome the
Windows semantics, but should at least do as much as can be done. Windows likes
to go part way in a random order and the die at the first sign of trouble.
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