El dt 25 de 11 del 2008 a les 13:12 -0500, en/na Dan Langille va
escriure:
> On Nov 25, 2008, at 2:10 AM, David Jurke wrote:
> 
> > The problem I have is with our large (expected to grow to several  
> > terabytes) database server. I’m told by the DBAs that the size and  
> > amount of activity on this database is such that putting the whole  
> > database into hot backup mode for the several hours it takes to back  
> > it up is a Bad Idea, it generates far too many log(?) files. The  
> > method they recommend is to put a single tablespace into backup  
> > mode, back that up, put it back to normal, repeat for each  
> > tablespace. The backup takes the same time, but doesn’t generate  
> > anything like the amount of log(?) files.
> 
> There is no way to dump interactively?  I'm a PostgreSQL fan and  
> creating a backup doesn't add overhead.
> 
> Are the DBAs sure that this won't create an inconsistent backup?  That  
> is, to restore, you are combining data from different times.  I'm sure  
> that transactions have occurred during that time... etc.

Backing up only Oracle datafiles ( tablespaces ) making up 'backup mode'
doesn't save you to backup an INCONSISTENT datafile. In backup mode, the
datafile blocks are modified AS USUAL, but the datafile header is
freezed, when turning on the tablespace 'bakup mode' off, the smon
process executes a recover of this datafile using the redo/archive info.

To get a recoverable database, you must put ALL tablespaces 'backup
mode' on, copy the archives, put them again on backup mode off and force
archiving of the current logfile, and copy all archives generated
between the tablespace modification and 'now'. OF course after that you
must backup a copy of control file, init parameters, etc...


USE RMAN

rman in 9i is able to know where is the tablespace highwatermark and
only backup the data before it ( with your method, you copy all
datafile, even it is empty of usable data ), it does compression on the
backup result.

rman in 10g is able to ( rman 9i + )  know the unused blocks under the
tablespace highwatermark, backing up only the used blocks


My 2 cents


Feel free to give my mail to your dbas, I'm always open to help ( I'm
usually stay on #oracle @ irc.freenode.net )

D.


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