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Home -> Community -> Mailing Lists -> Oracle-L -> RE: may not be necessary -- was RE: Oracle DB Backups on SAN
We use the 'shadow mirror' process on a Hitachi SAN (with
Oracle 8.1.7 on Solaris 8 and Veritas VxFS) successfully to refresh
our development db without a suspend, or even hot backup mode.
After the hair that I didn't pull out turned gray (though
I am not willing to detail the incompetence on a semi-public
list), we got the hardware/file system set up correctly and
we have done this several times with no trouble.
One issue I had with Hitachi support was that they insisted I
had to suspend the database at the time of the split when we
were seeing data corruption that was clearly unrelated to Oracle
behavior. It turned out to be low level misconfiguration, I believe
at the Veritas file system level. I never got a satisfactory
explanation.
Here is my current (possibly inaccurate) understanding of the
process. I would be more than happy to be corrected on any of
the details.
The shadow mirror process is 'atomic' in the sense that there is
some kind of journaling so that when the mirror is split, it is
done so that the shadow is a copy of the disk at a particular
time, so it looks like the disk would look after a crash or a
shutdown abort. Oracle crash recovery has worked as advertised,
which is sufficient for our development db needs. If we do get a
bad mirror, we would be able to resync and resplit quickly. But
as I said, we've done this without incident at least 8 or 9
times. The only times we've had to resync and resplit were due
to human error.
If you are using Shadow mirror, and this is for backup purposes,
you may want the extra security of hot backup. But the mirror
split should not cause split blocks, so I'm not sure that it
would actually do much for you. To be honest, I haven't thought
through all the ramifications of using this as a backup method.
If you're not using Shadow mirror, but some other mirror method,
the above may not apply.
Hope this helps.
-Chris
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Author: Sarnowski, Chris
INET: csarnows@CuraGen.com
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