[Udpcast] Cloning Live Machine

Donald Teed dteed at artistic.ca
Tue Jul 20 21:00:11 CEST 2004

On Tue, 20 Jul 2004, Christopher Curtis wrote:

> Actually, in practice, you'll probably find that most of the time it 
> "just works".  However, if you have LVM installed, you could make a 
> snapshot of the image before you udpcast it.  Most of the data that's 
> not written to disk is "inoccuous" stuff such as logfiles.  However, I 
> wouldn't try this to make a copy of a running database, for instance.

Yes, this is what I am assuming.  If the person states that
the system must be live, it must be a production system of
some type, providing an essential service that is accessed
at all times of the day.  There is a good possibility of files
being in a state of being half written, and so on.

It won't even simulate a power loss, because a low level
copy of the entire drive will capture parts of the drive
at a different time.  In the case of something like a database,
there are several files in use, and some of them may be large.
It might even take a few seconds to minutes to capture a
single file on the low level dump, and during that time the
file has been updated in several different parts at different
times.  It would lead to a file of garbage and thus
a corrupted database.

A database is a easy example to understand, but the same
could be true of any file that is being written on the
system, including the filesystem table!  Unless you are
just fooling around, don't do it!

--Donald Teed

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