Re: Minimizing backup induced downtime

On Jul 12, 1:33 pm, Alexander Skwar <alexan..._at_skwar.name> wrote:
> Hello.
>
> As you might have noticed :), I'm trying to learn RMAN and am thinking
> about how to use it right for our backups. As it seems to me right now,
> the use of RMAN will make the downtime because of backup *LARGER* than
> it is right now.
>
> Let me explain how I currently do a backup.
>
> 1) Shut down application, which uses Oracle as a backend
> 2) Shut down Oracle
> 3) Create filesystem snapshots with ZFS on Solaris 10
> 4) Start backup to tape of filesystem snapshots. When done, remove snapshots
> 5) Startup Oracle
> 6) Startup application
>
> The step 4 is run in the background. Because of this, the actual
> downtime is very small (a matter of seconds. At most, it's 1 minute).
> I'm currently shutting down everything, so that the files on backup are
> in a consistent state.
>
> I'm now thinking about how to fit RMAN into this picture. I think it
> might look something like this:
>
> 1) Shut down application, which uses Oracle as a backend
> 2) Have RMAN create backup of database
> 3) Create filesystem snapshots with ZFS on Solaris 10
> 4) Start backup to tape of filesystem snapshots. When done, remove snapshots
> 5) Startup application
>
> Here, step 3 is in background. But I cannot start step 3, before step 2
> is actually finished. Because of this, the downtime of the application
> will be larger, won't it? Granted, I don't have to shutdown the
> application, but then I don't know that I'm in a consistent state. Suppose
> that I do not shutdown the app while RMAN is running. Then a user comes,
> adds/deletes/modifies something. This modification is then, of course, not
> part of the backup I'm doing at this run. Even worse - the FS snapshot
> doesn't "harmonize" with what's in the DB (the application creates/deletes
> files in a so called "vault", which is some directory on the server).
>
> Because of all of this, I'd like to shutdown the application while RMAN
> is running.
>
> In such a scenario/setup, wouldn't RMAN make the downtime larger? Or am
> I overlooking something completely (which might of course be true)? Hm,
> right now, I'm pretty much thinking, that a shell script based backup
> (as I'm currently doing) is a better approach, don't you think?
>
> Regards,
>
> Alexander Skwar

I really don't know why you are dismissing RMAN, without even having read the documentation sufficiently.
If you are convinced you have a 'better approach', I suggest you stay in the Stone Age of Shell Scripts and stop bothering this forum. Obviously, RMAN can cope with the 'split-mirror' technique you described, but you obviously don't want to hear that, as you already have dismissed RMAN, without even using it.

--
Sybrand Bakker
Senior Oracle DBA