IBM sub capacity licensing can halve a PVU bill, but only if the IBM License Metric Tool is installed and reporting on time. Miss the rule and IBM counts full capacity. Here is the buyer side read.
Sub capacity is the difference between licensing the cores IBM software actually uses and licensing every core in the data center, and ILMT is the one thing that holds it.
Most IBM middleware is licensed in Processor Value Units. A PVU is a per core unit weighted by processor type, so the same core count can carry different PVU totals on different chips.
Full capacity counts every core in the physical server. Sub capacity counts only the cores allocated to the IBM software, which on a virtualized host is usually far fewer.
IBM defines the metric and the eligibility rules in its Passport Advantage terms and the License Metric Tool documentation.
The choice between the two is the single largest number in an IBM PVU estate. On a large virtualized host running one small IBM workload, the difference is dramatic.
Different processors carry different PVU per core ratings. The same physical core count can produce a higher or lower PVU total depending on the chip family.
Full capacity versus sub capacity on a virtual host
| Scenario | What is counted | Requirement | Relative cost |
|---|---|---|---|
| Full capacity | All physical cores | None | Highest |
| Sub capacity eligible | Allocated virtual cores | ILMT reporting | Lowest |
| ILMT stale | Reverts to full capacity | Reports lapsed | High |
| Host without agent | Full capacity for that host | Agent missing | High |
The IBM License Metric Tool is the system of record for sub capacity. Without it, you have no standing to claim anything less than full physical capacity.
The rules are specific and unforgiving. Meet them continuously and your eligible position holds. Miss them and the position reverts.
ILMT must generate capacity reports at least every ninety days, and you must retain those reports for two years. Both conditions matter at audit.
The common failure is not a missing tool, it is a new host added without the agent. That single uncovered host can be counted at full capacity.
Audit your host inventory against the ILMT agent list regularly so new infrastructure does not silently break eligibility.
The trap is simple. If ILMT is not in place or its reports are stale, IBM is entitled to count full physical capacity, and on a virtualized estate that is often a multiple of your real usage.
Buyers discover the gap at audit, when there is no time to retrofit two years of reports. The position cannot be rebuilt backward.
The standard advice is that installing the IBM License Metric Tool once is enough to secure sub capacity, so teams treat it as a setup task and move on. We disagree. In roughly one in three IBM estates we reviewed in 2024 and 2025, ILMT was installed but its reports had lapsed past ninety days or new hosts ran without the agent, which handed IBM a full capacity position worth several times the eligible number. The buyer side move is to treat ILMT as a continuous control, audit host coverage every quarter, and retain two unbroken years of reports as your evidence base.
IBM ties sub capacity eligibility to ILMT compliance. See IBM's sub capacity licensing information and the Db2 product terms for the counted metrics.
Source: Redress Compliance advisory engagement file, 2024 to 2025.
On IBM PVU the host you spun up last quarter without the agent is the one the auditor counts at full capacity.
The protection is operational, not contractual. Keep ILMT reporting clean, cover every host, and retain the evidence. Then the renewal and the audit both go your way.
Pull two years of ILMT reports and reconcile them against your host inventory before IBM asks. A clean, complete report set is what holds your eligible number.
White Paper · IBM
IBM ILMT and Sub Capacity Guide
The buyer side framework for IBM License Metric Tool deployment and sub capacity compliance. Read it free.
Sub capacity lets you license only the cores allocated to IBM software in a virtualized environment rather than every core in the physical server. It applies to most Processor Value Unit licensed middleware and depends on the IBM License Metric Tool being installed and reporting.
A Processor Value Unit, or PVU, is IBM's per core licensing metric weighted by processor type. The same number of cores can carry different PVU totals depending on the chip family, because IBM assigns a per core rating in its PVU table.
The IBM License Metric Tool must generate capacity reports at least every ninety days, and you must retain those reports for two years. Every virtual host running eligible IBM software must also run the ILMT agent for the sub capacity position to hold.
If reports lapse past ninety days or a host runs without the agent, IBM has standing to count full physical capacity instead of sub capacity. On a virtualized estate that can be a multiple of your real usage, and it cannot be rebuilt backward at audit time.
The gap between sub capacity and full capacity on a virtualized host is often a multiple rather than a margin. In reviews we ran the full capacity exposure commonly landed at two to five times the eligible number when ILMT failed.
No. ILMT is a continuous control, not a one time setup. The common failure is a new host added without the agent or reports that lapse past ninety days, both of which break eligibility, so coverage must be audited every quarter.
Cap the virtual cores allocated to the IBM software to what the workload actually needs, since sub capacity counts allocated cores. Right sizing the allocation and keeping ILMT clean together produce the lowest defensible position.
Pull two years of ILMT reports and reconcile them against your live host inventory before IBM asks. A complete, continuous report set is the evidence that you owe sub capacity rather than full physical capacity.
PVU sub capacity math, the ninety day ILMT reporting rule, the full capacity trap, and the renewal levers that hold your eligible position.
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