Rman backup Compress question

Question

Oracle ver 10.2.0.1 -- 24/7
250G database. I ran the script
run {
allocate channel c1 type disk format '/hotbackup/%d/db_%d_t%t_s%s_p%p%c';
set limit channel c1 kbytes 2024800;
sql "alter system archive log current";
backup as compressed backupset
incremental level 0
filesperset=20 (database include current controlfile);
release channel c1;
# Backup all archive log files
allocate channel t1 type disk format '/hotbackup/%d/al_%d_%s_%p%c';
backup as compressed backupset filesperset=20 (archivelog all delete input);
release channel t1;
delete noprompt backup completed before 'sysdate-1';
And the backup file is still around 220G. Is there another way to compress? Anybody have an idea how to make the backup smaller?
Thank You

Answer 1

How many CPU's does your server have?
And why don't you let RMAN choose the default's regarding the files per set, the backup set piece size, etc. Whenever you run a compressed backup, RMAN would normally use at approx.12% of CPU per channel. A 45hr backup time is clearly unacceptable that too when it is a 24/7 database but as your are using a single channel, which might be the culprit. I would suggest to use about 4 channels (depending on your CPU load) and do not put any restrictions on the files per set and backup set piece size.
We do a compressed backup to disk of a 230G database on a 8 proc server with 4 channels allocated and the backup normally completes in about 1.45 hours and the FULL backup size produced is around 30G ( level 0 is a FULL backup).