On Fri, 2 Dec 2005, Gabriel Gunderson wrote:
I've been reading this thread and wondering if you are talking about two
different things.
It seems that Nicholas is saying that an rsync is not enough to back up
a server that has important and changing temporary data written to
files.
It seems that Ross wants to know if there is any harm in rsyncing the
directories where that data lives.
What I'm wondering is this:
on a typical Linux server, if you just do an rsync of the entire drive at
2 AM, and the live hard drive bites the dust next day, if you restore the
dead drive from the rsync'd backup:
a) What sort of things are not going to just magically work, and
b) What sort of things are going to possibly have data loss because the
drive was not read-only when rsync'd?
My own impression of (a) is that there are a lot of things that won't just
magically work; you'll be lucky if you get a bootable system out of a raw
file-copy. But reinstall Linux and possibly a few of the programs and
you're good to go. I'm not so concerned about this one.
The answer to (b) is much more worrisome to me ... I understand that
databases could have data loss because you're rsyncing in the middle of
whatever the database happens to be doing at that particular moment. I
solve this problem by dumping the database to a flat file and backing that
up instead. But what other sorts of things might have data loss? For
example, if a mail file was being written to at the exact moment when you
rsync'd, and that caused the remote backup file to be deleted or zeroed
out or corrupted or whatever.
I think we've established that mail files are ok because if you rsync
while it's being written to, you'll simply get a backup of the old version
of the file (not an empty or deleted file). But are there other programs
where you *will* get data loss in this sort of scenario?
~ Ross
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