The AS400, iSeries and IBM i Power Systems are famous for their resilience and ability to handle really large files sizes and thousands of users at the same time. Database files (aka TABLES) can be massive or even set to SIZE(NOMAX).

I was just in an interesting meeting where the question was “What if application vendors have set their file sizes to *NOMAX in the mistaken belief that they will never fill up?” and then someone else asked “if a file is size(NOMAX) how does it reach a maximum size at around a terrabyte?”

Nomax should mean nomax right?

Erm….. Nope!

It’s just not quite that simple.

IBM i limits object sizes for several reasons:

1. Performance Optimization: Large objects can significantly slow down system performance, especially during backup and recovery operations. By limiting object sizes, the system can maintain optimal performance
2. Storage Management: IBM i systems have finite storage resources. Efficiently managing object sizes helps ensure that storage is used effectively and prevents any single object from consuming too much space
3. System Stability: Limiting object sizes helps prevent system crashes or slowdowns that could occur if an object grows too large. This is crucial for maintaining the overall stability and reliability of the system
4. Compatibility and Interoperability: Some applications and processes may have their own limits on object sizes. By enforcing system-wide limits, IBM i ensures compatibility and smooth operation across different applications and processes

These limits are designed to balance performance, storage efficiency, and system stability, ensuring that the IBM i system runs smoothly and reliably.

So, what size does NOMAX really mean?

IBM have really fat object size limits to prevent any roque job from simply looping and looping and creating an ever-growing object size which will eventually fill all the disk and bring your poor power system crashing down on its knees. Nobody likes that idea!

The IBM i system has several limits depending on the type of object and the system configuration:

• Maximum number of objects in a library: Approximately 360,000 objects
• Maximum size of a single object: This can vary, but for many objects, it can be up to 1 TB (terabyte)
• Maximum number of rows in a table: Up to 4,294,967,294 rows
• Maximum size of a journal receiver: Up to 1 TB

These limits can vary based on the specific version of the IBM i system and its configuration. So, let’s try to dive in and find the numbers for the current release : V7R5M0

• PDF file for Maximum capacities
  You can view and print a PDF file of this information.
• Cluster limits
  The IBM i system limits for clusters include cluster software limits, and OptiConnect limits.
• Communications limits
  The IBM i system limits for communications include general communications configuration limits, SNA limits, TCP/IP limits, and communications trace service tool limits.
• Database and SQL limits
  Several types of IBM i system limits are related to database and SQL.
• File system limits
  This topic contains the values for the system limits that are related to file systems. They include limits on the number of documents in a folder, the size of a document, the size of a stream file, and others.
• Journal limits
  Some IBM i system limits relate to journals, such as the size of a journal receiver, the length of a single journal entry, and the maximum sequence number for journal entries.
• Save and restore limits
  Some IBM i system limits relate to save and restore, such as limits for the size of a save file and the size of an object that can be saved.
• Security limits
  Some IBM i system limits relate to security, such as limits on the length of passwords and the number of user profiles on a system.
• Work management limits
  There are IBM i system limits that are related to work management, such as limits on the number of jobs on a system, the number of active subsystems, and the number of jobs in a subsystem.
• Miscellaneous limits
  There are some other IBM i system limits, such as the number of basic disk pools, the size of a user space, and the size of a message queue.
• Related information for Maximum capacities
  IBM Redbooks® publications, Web sites, and other information center topic collections contain information that relates to the Maximum capacities topic collection. You can view or print any of the PDF files.

Start by using your IBM i Disk Information to find the list of fattest objects on your machine.

Or even the quick and easy SQL view to grab the top offenders: