If you’re coming from a Windows or general IT background and diving into the IBM i world, you’ve probably heard of ASP, System ASP, and IASP. These terms can feel confusing at first, but they’re simply IBM i’s way of organizing disk storage - just like drives and volumes in Windows.
Let’s break it down using concepts familiar to Windows users.
What is an ASP?
An ASP (Auxiliary Storage Pool) is IBM i’s way of grouping disk space into logical pools. Think of it like a drive volume in Windows — like your *C:* or *D:* drives.
There are three main types:
- System ASP (ASP 1) – Like your C:\ drive where Windows is installed.
- User ASPs – Additional volumes created within the same system.
- IASPs – Think of these like external or detachable drives that you can plug into different machines.
System ASP and User ASPs (Non-Independent ASPs)
These ASPs are part of the core system storage. They are always online when the system is up - much like how your C:\ drive is always available in Windows.
Think of it like this:
System ASP = C:\ Drive (OS + default files)
User ASPs = D:\ or E:\ Drives (Extra volumes within the same system)
- Contain operating system, default libraries like QSYS.
- Always active and cannot be detached from the system.
- Ideal for standard installations and learning environments.
What is IASP?
An IASP (Independent ASP) is a separate storage pool that can be mounted or unmounted — just like how you plug in an external USB drive or a network-attached volume in Windows.
IASP = External USB Drive or a VHD file
You can “attach” it to one system, do your work, and then “detach” and move it to another.
Key Features of IASP:
- Not tied to the system ASP.
- Can be varied on/off — similar to mounting/unmounting a volume.
- Great for disaster recovery, high availability (HA), and application isolation.
Windows Analogy Table
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IBM i Concept
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Windows Analogy
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Description
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System ASP (ASP 1)
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C:\ drive
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OS + default programs
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User ASPs
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D:\, E:\ (part of same system)
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Additional volumes
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IASP
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External drive or VHD
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Detachable, independent volume
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Vary On / Vary Off
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Mount / Unmount drive
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Activate or deactivate the storage
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Switching IASPs
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Plug external drive into another PC
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For HA or migration
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Why Use IASP?
You might use IASP when:
- You want to isolate applications and their data.
- You need fast switchover in case of system failure (HA setup).
- You’re managing multiple environments on shared infrastructure.
- You need to move workloads between LPARs or physical systems.
Summary
For everyday use and learning, the System ASP (ASP 1) and User ASPs are more than enough. But as your environment scales or needs more flexibility, IASPs become powerful tools for separation, resilience, and efficiency — much like external or virtual drives in Windows.