# IBM i Disk Growth and Capacity Forecast Calculator

> Source: https://netray.co/tools/ibm-i-disk-growth-and-capacity-forecast-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Forecast how many months until IBM i auxiliary storage reaches your threshold, using current use, capacity and monthly growth.

## Category

erp-operations

## Erp

Oracle JD Edwards World

## Audience

- IBM i administrator
- IT manager
- Capacity planner

## Tool

**Kind:** calculator

**Currency:** $

**Inputs:**

#### Total usable disk capacity

**Key:** capacity

**Type:** number

**Default:** 4000

**Min:** 1

**Step:** 100

**Unit:** GB

**Help:** Total auxiliary storage in the system pool you plan against.

#### Currently used

**Key:** used

**Type:** number

**Default:** 2300

**Min:** 0

**Step:** 50

**Unit:** GB

**Help:** Current used storage, not including free space.

#### Monthly growth rate

**Key:** growth

**Type:** number

**Default:** 2.5

**Min:** 0

**Max:** 30

**Step:** 0.1

**Unit:** %

**Help:** Average monthly increase in used storage, measured over at least six months.

#### Planning threshold

**Key:** threshold

**Type:** select

**Default:** 0.8

**Options:**

##### 70% full

**Value:** 0.7

##### 80% full

**Value:** 0.8

##### 85% full

**Value:** 0.85

##### 90% full

**Value:** 0.9

#### Planned one-time purge

**Key:** purge

**Type:** number

**Default:** 200

**Min:** 0

**Step:** 10

**Unit:** GB

**Help:** Data you expect to archive or delete once.

#### Cost per added GB

**Key:** cost_gb

**Type:** number

**Default:** 3

**Min:** 0

**Step:** 0.5

**Unit:** $ per GB

**Help:** Use your quote, including installation and support.

**Outputs:**

#### Current utilization

**Key:** used_pct

**Expr:** if(gt(capacity,0), used / capacity * 100, 0)

**Format:** percent

#### Threshold in GB

**Key:** limit_gb

**Expr:** capacity * threshold

**Format:** number

#### Used after purge

**Key:** net_used

**Expr:** max(used - purge, 0)

**Format:** number

#### Months to threshold without purge

**Key:** months_now

**Expr:** if(and(gt(growth, 0), gt(limit_gb, used)), ln(limit_gb / used) / ln(1 + growth / 100), 0)

**Format:** months

**Primary:** true

**Description:** Zero means the threshold is already reached or growth is zero.

#### Months to threshold with purge

**Key:** months_purge

**Expr:** if(and(gt(growth, 0), gt(limit_gb, net_used), gt(net_used, 0)), ln(limit_gb / net_used) / ln(1 + growth / 100), 0)

**Format:** months

**Primary:** true

#### Used storage in 12 months

**Key:** needed_12

**Expr:** used * pow(1 + growth / 100, 12)

**Format:** number

#### GB to add to stay under threshold in 12 months

**Key:** buy_gb

**Expr:** max(needed_12 / threshold - capacity, 0)

**Format:** number

#### Estimated cost of added disk

**Key:** buy_cost

**Expr:** buy_gb * cost_gb

**Format:** currency

**Chart:**

#### Used storage after 12 months vs monthly growth rate

**Type:** line

**X:** growth

**From:** 0

**To:** 10

**Steps:** 20

**Series:**

- needed_12

**Disclaimer:** Planning estimate using compound monthly growth. Real growth is lumpy because of month-end, journals, spooled output and projects. Use measured data from your own system and leave headroom for save operations and temporary storage.

## Content

**Intro:** Running out of auxiliary storage on IBM i is a serious outage risk, and the warning signs are slow. This calculator estimates when your used storage will cross a threshold and how much disk you need to add to stay under it for a year.

**Sections:**

#### How to use it

**Body:** Enter total capacity and current used storage from your system status. For growth, measure used storage monthly for at least six months and use the average percentage change. Pick a planning threshold. Many sites plan to stay below roughly eighty percent because performance and save operations suffer as disks fill. Add a planned purge if you have an archive project. The calculator returns months to threshold with and without that purge.

**Bullets:**

- Use measured growth, not vendor estimates
- Include journal receivers and spooled output in used storage
- Add headroom for restores and temporary objects
- Recalculate quarterly

#### The formula

**Body:** Growth is modeled as compound monthly growth. Months to threshold equals the natural logarithm of threshold storage divided by used storage, divided by the natural logarithm of one plus the monthly growth rate. Used storage after twelve months is used storage times one plus growth to the power of twelve. Disk to add is that figure divided by the threshold, minus current capacity.

#### Reading the results

**Body:** If months to threshold is below your budget cycle or lead time for hardware, act now. A purge can buy time, but the date moves only once because growth resumes afterward. Compare the cost of added disk with the cost of an archive project and the cost of a risky outage. The chart shows how sensitive the twelve-month figure is to growth rate.

#### Common mistakes

**Body:** Using one very good or bad month as the growth rate gives a misleading answer. Another mistake is ignoring journal receivers, which can dominate growth when journaling is turned on without a cleanup policy. Also remember that a fuller system makes backups, reorganizations and restores harder. Plan for the worst day, not the average day.

**Cta:** Netray can help analyze which libraries and files are driving growth and which are safe archive candidates.

**Faq:**

#### What utilization is too high on IBM i?

**Answer:** There is no single rule, but many administrators plan to stay under about eighty percent and treat above ninety as urgent. Performance, saves and reorganizations get harder as storage fills, so confirm your own threshold with your support provider.

#### How do I measure monthly growth?

**Answer:** Record used storage at the same point each month for six to twelve months, compute the percentage change between months, and average the results. Remove one-off events such as a large data load so they do not distort the trend.

#### Does a purge fix the problem?

**Answer:** It moves the date out once. If growth continues at the same rate, you reach the threshold again. Combine purges with retention rules so that growth itself slows.

#### Is the result a guarantee?

**Answer:** No. It is a planning estimate based on a steady growth rate. Actual use changes with business cycles and projects, so review the forecast regularly.

## Search terms

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