Raid 5 (was: Mounting of Linux volumes)
ross at agilestudios.com
Fri Dec 2 10:58:33 MST 2005
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
> 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?
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