AS/400 Disk Storage Growth Forecast Calculator
On IBM i, a system that runs out of disk does not degrade politely. Jobs fail, saves stop, and recovery can be slow. This calculator forecasts when you hit your own safe limit so you buy or archive before then.
Your numbers
Total disk capacity of the system auxiliary storage pool, as shown on WRKSYSSTS or WRKDSKSTS.
Used storage excluding journal receivers if you can separate them.
Days of receivers kept before they are saved and deleted.
Many sites alert well before the ASP threshold, to leave room for saves and temporary storage.
Your results
Planning model with compound growth. Real growth is lumpy. Leave room for save files, temporary storage and rebuilds.
Extra disk needed at horizon vs data growth
Sweeps Annual data growth from 0 to 60, holding your other inputs fixed.
Library size and growth report
Optional: a read-only report of storage by library and month.
Optional. The tool and every export work without this. No spam.
How to use it
Read total capacity and percent used from WRKSYSSTS or WRKDSKSTS. Estimate annual growth from three or more year-end snapshots of used storage, not from a single month. Then enter journal receiver volume and retention separately, because they are large, steady and under your control. Choose a safe utilisation that leaves room for save files and rebuilds, often well under the system ASP threshold.
The method
Journal space is receiver volume per day times retention days. Usable room for data is capacity times the safe percentage, minus that journal space. If data grows at rate g per year, years left equal ln(usable divided by data) divided by ln(1 + g). Extra disk at the horizon is the future data plus journal, divided by the safe fraction, minus current capacity.
- Data in JDE World history and ledger files such as transactions and ledger detail tends to grow steadily
- Archive and purge can change the growth rate, so test with a lower value
- RAID overhead is not modelled: use usable capacity
How to read it
If years left is under two, you need a plan for either archiving or adding disk, and procurement lead times matter. The chart shows the extra disk required at the horizon for each growth rate, which helps you decide if a purge project is worth more than new drives. Compare the cost of the extra gigabytes with the cost of the purge work before choosing.
Common mistakes
Mistakes include forgetting journal receivers, which can hold more than the data they protect, counting save files stored on the same disks, and using a threshold of 90 percent or more. Also remember that a restore after a failure may need room for both the old and the restored data.
Frequently Asked Questions
Why separate journal receivers?
They are generated at a fixed daily rate and deleted on a schedule, so they behave differently from business data. Separating them gives a clearer picture and shows how much retention policy changes disk needs.
What threshold should I use?
Choose a level that still leaves room for save files, temporary storage and a spike. Many sites alert at 70 to 80 percent. Your own incident history is the best guide.
Can I use it for a hosted IBM i?
Yes. Enter the storage you have been allocated. The result then tells you when to ask the provider for more and what it will cost.
What if growth is negative after a purge?
Use zero. The model then shows no time limit, and you should plan on measured growth after the purge completes.
If you want a read-only report of your largest files, libraries and growth by month, Netray can produce one from your IBM i system.
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