Using 90 Days of Usage for Rightsizing Recommendations in VCF Operations 9

In a previous post I walked through configuring VCF Operations 9 capacity policies to align with a 90-day planning window. If you followed that guide, the good news is that rightsizing recommendations share the same underlying policy — Risk Level, Time Remaining thresholds, and buffers all feed directly into the rightsizing engine.

So why a separate post? Because rightsizing is a different workflow with its own nuances. Capacity planning asks “when will my clusters run out of room?” Rightsizing asks “are my individual VMs sized correctly for what they actually use?” The policy is the same foundation, but how you consume and act on the results is completely different.

Note on naming: VCF Operations 9 is the successor to VMware Aria Operations (formerly vRealize Operations). The same rightsizing concepts apply across versions but some UI labels may differ.

How the Rightsizing Engine Uses Your 90-Day Policy

When you configured your capacity policy with a Conservative risk level and a 90-day critical threshold, you also configured the rightsizing engine. Here is how those settings translate:

• Risk Level = Conservative → The rightsizing engine uses the upper bound of projected VM utilization. This means it will not recommend downsizing a VM unless it is genuinely underutilized even during peak periods within your 90-day window. This prevents the classic “we rightsized the VM and now month-end processing is slow” problem.

• Time Remaining thresholds → The “Recommended Size” metric is calculated to ensure the VM maintains a healthy state for the duration defined by the Green Time Remaining Score Threshold, plus an additional 30 days. With a 90-day critical threshold, the engine is projecting VM resource needs well beyond the immediate term.

• Peak Focused = Enabled → The engine accounts for utilization spikes in its recommendations. A VM that idles at 10% CPU for 85 days but spikes to 80% during month-end will not be flagged as massively oversized.

If you have not yet configured these policy settings, start with the capacity policy guide first — those same settings power rightsizing.

What’s Different for Rightsizing: Business Hours

One policy setting that is particularly important for rightsizing but less so for cluster capacity is Business Hours. Where capacity planning looks at the cluster as a whole around the clock, rightsizing focuses on individual VM behavior — and many VMs have workloads that only run during specific hours.

If your line-of-business applications are only active during 8 AM – 6 PM on weekdays, you want the rightsizing engine to project demand based on those hours, not the idle weekend utilization that would drag the average down and lead to undersized recommendations.

To configure Business Hours:

1. Open your policy in Infrastructure Operations > Configuration > Policies > Policy Definition.
2. Select your production policy (e.g., Production Clusters – 90 Day Capacity Window).
3. Navigate to the Capacity section.
4. Look for the Business Hours setting.
5. Define your operational hours (e.g., Monday–Friday, 08:00–18:00).
6. Save the policy.

With Business Hours enabled, the capacity engine and rightsizing engine will weight the utilization data from those hours more heavily, which directly improves the accuracy of the recommendations for workloads that follow a predictable schedule.

Tip: If you have 24/7 workloads (databases, web servers), keep Business Hours disabled for those VMs by applying a separate policy without Business Hours defined.

Understanding the Recommendation Caps

Before you act on any rightsizing results, it is important to understand that VCF Operations applies built-in safety limits to its recommendations:

These caps exist to prevent drastic changes that could destabilize workloads. If a VM is severely oversized — for example, allocated 16 vCPUs but only ever using 2 — the tool will recommend reducing to 8 vCPUs on the first pass. After the change is applied and another 90-day observation period passes, it may recommend a further reduction.

This is why rightsizing is an iterative process, not a one-time event. Plan for at least two or three cycles to fully right-size an environment that has significant sprawl.

Consuming the Rightsizing Results

Now that your policy is tuned for 90 days of usage data, here is how to find and act on the recommendations.

Finding Oversized and Undersized VMs

1. Navigate to Capacity > Optimize > Rightsize.
2. The view will show VMs flagged as Oversized, Undersized, or Powered Off based on your policy settings.
3. Filter by cluster or custom group to focus on your production workloads.

Key Metrics to Review

For each VM, pay attention to these metrics:

• Recommended vCPUs — The engine’s suggestion based on 90 days of projected peak demand (Conservative) or average demand (Aggressive).
• Recommended Memory — Same projection logic applied to RAM.
• CPU Demand % — What the VM is actually using relative to what is allocated. A VM with 8 vCPUs at 5% demand is a strong downsizing candidate.
• Memory Active % — Active memory versus allocated. Be cautious here — memory rightsizing is more sensitive than CPU because memory pressure can cause ballooning or swapping.

Exporting Rightsizing Data for Quarterly Reviews

For quarterly capacity reviews, export the rightsizing recommendations directly from the Rightsize page:

1. Navigate to Capacity > Optimize > Rightsize.
2. Apply your filters (cluster, custom group, or object type) to scope the results to your production workloads.
3. Use the Export option to download the rightsizing data as a CSV or PDF.
4. For a recurring view, use the out-of-the-box VM Rightsizing Details dashboard — search for it under Dashboards — which provides a consolidated view of potential savings and reclaimable capacity.

This export becomes the artifact you bring to your quarterly capacity review meeting, alongside the capacity projections from the first blog post.

The Rightsizing Workflow: A Practical Approach

Rightsizing an entire environment in one pass is risky. Here is a phased approach that works well with a 90-day observation window:

Phase 1 — Identify Quick Wins (Week 1–2)

Focus on the obvious outliers first:

• VMs with CPU Demand < 10% and 8+ vCPUs allocated.
• VMs with Memory Active < 20% and 16+ GB allocated.
• Powered-off VMs that have been off for 30+ days — these are candidates for decommissioning, not rightsizing.

Phase 2 — Apply CPU Changes First (Week 3–4)

CPU rightsizing is generally safer than memory rightsizing because:

• vCPU changes can often be performed with a scheduled reboot.
• The performance impact of reducing vCPUs is more predictable.
• Over-allocation of vCPUs can actually hurt performance due to CPU scheduling overhead (co-stop and ready time).

Apply the recommended CPU changes to your quick-win VMs and let the environment run for at least one full collection cycle before moving on.

Phase 3 — Evaluate Memory Changes (Week 5+)

Memory is trickier:

• If a VM loses memory headroom, it may start ballooning or swapping, which causes latent performance issues that do not show up immediately.
• Always leave a 10–15% memory buffer above the recommended amount.
• Monitor the Balloon and Swap Used metrics for at least a week after making changes.

Phase 4 — Observe and Iterate (90 Days)

After the initial round of changes, let the environment run for a full 90-day cycle. The engine will re-evaluate the VMs based on their new configuration and may recommend further adjustments. This is normal — rightsizing is iterative by design.

Bringing It All Together

If you configured your capacity policy using the previous guide, you already have 90% of the rightsizing foundation in place. The additional steps for rightsizing are:

Why This Matters

Every oversized VM is wasted capacity that could defer a hardware purchase. Every undersized VM is a performance risk that could lead to an outage.

With a 90-day rightsizing model you can:

• Reclaim capacity without guessing — recommendations are backed by 90 days of real usage data.
• Avoid month-end surprises — Conservative + Peak Focused ensures cyclical workloads are respected.
• Build a repeatable process — quarterly rightsizing reviews become a standard part of your capacity management cadence.
• Quantify savings — the delta between current allocation and recommended allocation is the capacity you can reclaim or redeploy.

References (VCF 9)

• Broadcom TechDocs — Optimizing Capacity and Improving Performance (VCF Operations 9.0)
• Broadcom TechDocs — Configuring Policies (VCF Operations 9.0)
• Brock Peterson — VM Rightsizing Minimums in VCF Operations
• Brock Peterson — Finding Capacity with VCF Operations