Factors

 

If backup pieces are very small, RMAN spends extra time opening/closing files, resulting in overhead and slower backups.

If backup pieces are too large and exceed filesystem or media manager limits, backups can fail or hang during writes or flushes.

Improper piece size might cause excessive I/O wait or network overhead if streaming backups or using tape devices.

Media manager throttling or channel bottlenecks due to file size mismatches.

I’ve gathered the necessary information related to our slow Oracle RMAN backup performance and have updated the Excel sheet accordingly.

The following key factors were taken into consideration during the analysis:

• Allocated channels

• Semaphores configured

• Average piece size for full/incremental backups

• nofile and nproc limits

• System page size

• shmmax and shmall values

• OS-level limits

Please review the updated file and let me know if there are any questions or if additional inputs are required.

Oracle RMAN Backup Performance Factors

Factor	Effect on Backup Speed	What to Check
Allocated Channels	More channels = better parallelism; too few = slow backup	`ALLOCATE CHANNEL`, `PARALLELISM` in RMAN scripts
Semaphores Configured	Insufficient semaphores can block or delay processes	Check `/proc/sys/kernel/sem`, `ipcs -s`, `sysctl` settings
Avg. Piece Size (Full/Inc)	Too small = overhead; too large = write delays or failures	RMAN logs, `MAXPIECESIZE`, backup piece sizes by level
nofile and nproc Limits	Low values limit open files or processes, may halt backups	`ulimit -n` (nofile), `ulimit -u` (nproc), `/etc/security/limits.conf`
System Page Size	Mismatch with DB block size may affect memory and I/O efficiency	`getconf PAGE_SIZE`, database block size (`db_block_size`)
shmmax / shmall	Low values can cause shared memory errors during large backups	`/proc/sys/kernel/shmmax`, `shmall`, `ipcs -m`
OS Limits	Global limits on files, memory, processes can restrict backups	`ulimit -a`, system-level limits in `/etc/security/limits.d/`

 

Factor	Effect on Backup Speed	What to Check
Backup Piece Too Small	High overhead, slower backup	MAXPIECESIZE setting, backup piece sizes
Backup Piece Too Large	Possible failures or slow flushes	Filesystem limits, media manager limits
OS Limits (ulimit/fs)	Backup stalls or fails if limits exceeded	ulimit -f, filesystem max file size
Number of Channels	Too few = slow, too many = overload	RMAN configured channels, storage capacity
Media Manager Settings	File size limits or throttling impacting speed	Coordinate with backup software team