On Thu, Jul 17, 2008 at 7:20 AM, David Barbour <david.barbour1@xxxxxxxxx> wrote: > Incremental backup (Level 1): System slows to a crawl. People complain. > Jobs take hours longer than expected (it's like they don't even start until > the backup completes). Statspack snapshot covering period when backup is > running shows top 5 timed events as follows: > > ... > What is the difference between disk access for the two types of backups? > Level 0 incremental (full) Oracle fills the buffer, sends it to tape Level 1 incremental Oracle scans files looking for blocks. When the buffer is full it is sent to tape Here's what I suspect is occurring: During the level 1 backup not a lot of changed blocks are being found, and Oracle is reading through datafiles as fast as possible. eg. io rates go up a lot. When doing a level 0, there are many more waits when writing to tape, and RMAN is not reading disk as often. Could be that level 1 backups are also killing the read cache on your IO system due to RMAN scanning the datafiles with far fewer interruptions for tape writes. Possible solutions? *Less frequent level 1 backups. Determine how many archive logs are being generated between Level 1 backups, perhaps you can rely more on the archive logs for recovery and reduce the frequency of Level 1 backups. This would be at the cost of recovery time however. *Upgrade to 10gR2 and use Block Change Tracking BCT was introduced in 10gR1, but was not fully baked until R2 -- Jared Still Certifiable Oracle DBA and Part Time Perl Evangelist