RE: rman backup to disk, mismatch in amount backed up to each cha nnel

  • From: "Hitchman, Peter" <Peter.Hitchman@xxxxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Fri, 22 Oct 2004 15:08:05 +0100

Thanks for the reply. Apparently we allocate two channels to speed things
up, but I don't know enough about the hardware set-up to be sure if the disk
I/O is acually separated out. Two of us have been looking into this issue
and if we cannot solve it we may well have to go the way you suggest.



-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Mark W. Farnham
Sent: 22 October 2004 14:53
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: rman backup to disk, mismatch in amount backed up to each

Unless your disk i/o communications pathways are truly separate, I would
actually suggest that you use only one channel and alternate the backup
destinations. I might even do this just for the reliability increase, even
if it takes a bit longer in the case where you really do have i/o pathways
that are non-interfering. Then alternate your channels each backup, which
preserves your ability to even out the storage size and means that if one or
the other destination fails, you still have an online backup. A belt and
suspenders. Now each alternation is going to the receiver about 75% full, so
you only have room for two copies. You'd need a little more space if you
wanted to cover the unlikely condition that "rman2" blows up (idle though it
may be at the time) during a backup to "rman1." You'd need a little more
space to have two complete at all times.

Now I did not really answer your question, which certainly would become
relevant if someone had, say, "rman1a", "rman2a", "rman1b", and "rman2b" and
they wanted to evenly split rman1a and rman1b on "a" days and evenly split
rman1b and rman2b on "b" days. Other than declaring the limit on each to be
only half the available space, I'm not sure how to do that, and I hope
someone more expert than me at rman operations chimes in.



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