Re: Estimating size of rman backup

nirav wrote:
> Hi,
> Size of my oracle 9.2.0.6 database is 26 gb..out of this , size of used
> space is 11 gb and rest is free space yet not used.
>
> Now if I go for rman backup, can I estimate that the size of backup set
> will be approx. 11 gb, since rman does not backup unused blocks? or is
> there some way to approximate the size of backup before beginning it?
>
>
> also on my server the total free space is 15 gb, but is divided into 2
> different mount points..in one mount point it is 8 gb and on the other
> one it is 5-6 gb, in that case can I specify 2 different backup
> locations for the backup?
>
> with thanks,

Depends. If you're certain you have 15 GB of space which has _never_ been used you can presume RMAN will backup 11GB of data blocks from your datafiles. However you haven't considered the space required for your controlfiles, or that required for your archivelogs; these two items will cause your backup set to exceed the 11 GB size you've originally determined.

I know of no way to estimate the overall size of an RMAN backup set; you COULD, I suppose, determine the total number of unused blocks in each tablespace, multiply by your block size and subtract that from your allocated tablespace size and then sum these adjusted sizes to give a rough estimate (as you've already done, apparently). You probably could come up with a method of creating even better estimates, but it would probably take you more time to calculate them than to actually run the backup. I would ensure I had enough disk space/tape space to backup the entire database rather than try to estimate what percentage of that total space you'll actually backup.

I would visit http://tahiti.oracle.com and start reading the RMAN backup and recovery guide for more information, and I would google for such topics and see what hits you return.

David Fitzjarrell Received on Mon May 29 2006 - 09:35:29 CDT