Backing up large Oracle databases often means wrestling with slow speeds and long backup windows. When a single datafile grows into hundreds of gigabytes or even terabytes, using just one channel can create an I/O bottleneck that drags down your entire operation. Oracle Recovery Manager (RMAN) addresses this challenge with its powerful section size feature—a way to split big files into smaller pieces so multiple channels can work together at once.
This guide explains what oracle rman section size is, why it matters for database administrators, how to set it up correctly, and how to monitor and optimize your backups for both speed and reliability.
What Is Oracle RMAN Section Size?
The section size parameter in Oracle RMAN lets you divide a large datafile into logical sections during backup operations. Each section covers a contiguous range of blocks within that file—not necessarily creating separate physical files on disk unless other settings like MAXPIECESIZE are used. By setting a section size, you enable RMAN to use multiple channels in parallel on different parts of the same datafile—a process called multisection backup.
For example, if you have a 500GB datafile and set SECTION SIZE 100G with five channels available, each channel can back up one 100GB segment at the same time. This approach is especially useful when dealing with bigfile tablespaces or any very large datafiles that would otherwise slow down your nightly backup window.
It’s important to note that while each section is processed independently by a channel, several sections may still end up inside the same backup piece unless you also specify limits like MAXPIECESIZE or FILESPERSET.
Why Section Size Matters in Backups?
Choosing an effective oracle rman section size can transform your backup strategy from sluggish to streamlined. Without specifying a section size, only one channel backs up each datafile at a time—even if you have many channels configured—leading to wasted resources and longer jobs.
By splitting large files into sections:
Multiple channels work together instead of waiting their turn
Backup times shrink because work gets distributed evenly
System load balances out across CPU cores and storage devices
You’re more likely to finish backups before business hours begin
For organizations managing very large databases (VLDBs), these benefits are crucial for meeting strict recovery point objectives (RPOs) and minimizing downtime risk.
However, using too small or too large a section size can cause problems—either overwhelming your system with coordination overhead or leaving some channels idle while others do all the work.
How to Set Oracle RMAN Section Size?
Setting oracle rman section size is straightforward but requires careful planning around syntax and resource allocation. You use the SECTION SIZE clause within the BACKUP command—but first make sure your environment has enough parallelism configured through channels.
Here’s how you might configure two disk channels for compressed backups:
CONFIGURE DEVICE TYPE DISK PARALLELISM 2 BACKUP TYPE TO COMPRESSED BACKUPSET;
BACKUP TABLESPACE system SECTION SIZE 200M FORMAT '/backup/rman/prddb/system_tbs_%s_%p_%t';
In this example:
The SYSTEM tablespace’s datafile gets divided into 200MB logical sections
Each channel picks up one section at a time
If the file is 1GB total, you’ll see about five sections processed in parallel
For more explicit control—especially in scripts—you might allocate channels manually:
RUN {
ALLOCATE CHANNEL ch1 DEVICE TYPE DISK;
ALLOCATE CHANNEL ch2 DEVICE TYPE DISK;
BACKUP DATAFILE 4 SECTION SIZE 10G FORMAT '/backup/rman/datafile4_%U';
}A few key rules:
If no SECTION SIZE is specified, RMAN uses its internal default (often resulting in single-channel processing)
If SECTION SIZE exceeds file size, multisectioning does not occur for that file
If your chosen value would create over 256 sections per file, RMAN automatically increases it so there are never more than 256 sections per file
You cannot combine SECTION SIZE with MAXPIECESIZE in one command; they are mutually exclusive
Remember: The minimum effective section size equals CEIL(FILE_SIZE / 256). Setting anything smaller has no effect since RMAN silently adjusts upward behind the scenes.
After running your backup job with SECTION SIZE enabled, always verify results by checking which pieces were created:
LIST BACKUP OF DATAFILE <datafile_number>;
You should see multiple pieces listed under each relevant datafile if multisectioning worked as intended.
How to Back Up Oracle Databases with Vinchin Backup & Recovery
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Step 1. Select the Oracle database to back up
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Oracle RMAN Section Size FAQs
Q1: Can I use different oracle rman section sizes within one script?
A1: No—you must run separate BACKUP commands if different files need unique SECTION SIZE values since each command applies its setting globally across included objects.
Q2: Does enabling oracle rman section size affect incremental backups?
A2: Yes—it works equally well whether backing up full sets or incrementals; just remember restore procedures must also account for multiple pieces per file when recovering incrementals later on!
Q3: What should I do if my storage device fills up mid-backup due to unexpected piece counts?
A3: Cancel job > Free space > Adjust SECTION SIZE upward > Restart job
Conclusion
Mastering oracle rman section size unlocks faster multi-channel backups—even across massive databases—with less risk of missed windows or overloaded systems along the way! With smart tuning plus regular validation checks built-in from day one—and solutions like Vinchin simplifying daily operations—you’re ready for whatever tomorrow brings in enterprise-scale protection.
