Sonia,
You may also find it helpful to use the I/O rate throttling feature of RMAN. This way you can limit the I/O rate in case you have to due a backup during times when the server is in use by many users. I use this technique in scripts which backup archivelog files separately from full database backups because this might have to occur during the daytime. Here is a link to an example script:

http://www.dotcomsolutionsinc.net/pr...ol901_85_.html

David Simpson
http://www.dotcomsolutionsinc.net