Why Forecasting & Capacity Planning Matters If you use SQL Diagnostic Manager every day to monitor performance, keep an eye on alerts, and troubleshoot blocking...
If you use SQL Diagnostic Manager every day to monitor performance, keep an eye on alerts, and troubleshoot blocking or slow queries, you are probably getting a very clear picture of what’s happening right now. But there is a second question that tends to catch DBAs off guard: what’s coming?
Storage volumes fill up. Databases grow. A table that looked fine last quarter is now responsible for most of your disk consumption. These problems rarely happen overnight — the trend is usually visible weeks or months ahead of time. The issue is that standard monitoring dashboards are built to answer “what is happening now,” not “when will this become a problem.”
SQL Diagnostic Manager already collects the disk, database, and table size history it needs to project growth forward. The Forecasting & Capacity Planning reports surface that history as forward-looking forecasts, so you can have the storage and budget conversation before you’re reacting to a crisis.
Reach for the forecast reports in any of these situations:
Note: You do not need to configure anything extra for these reports to work. SQL DM is already collecting the size data they rely on. If your instances are monitored, you are ready to run a forecast.
SQL Diagnostic Manager includes three reports under the Plan reports section, each answering a progressively more granular question:
| Report | Question It Answers | Best Used When |
| Disk Space Usage Forecast | How much free space will this volume have, and when might it run low? | You want a volume-level view across all databases sharing a drive |
| Database Growth Forecast | Which databases are growing fastest, and by how much? | You need to identify which databases are driving volume growth |
| Table Growth Forecast | Which specific tables inside a database are responsible for growth? | A database is growing fast and you need to find the root cause |
These three reports are designed to be used together in a drill-down workflow: start at the disk level, identify the databases driving growth, then drill into the specific tables inside those databases.
Each report asks you to choose a forecasting type before it runs. Choosing the right type makes a meaningful difference in how useful the output is.
Linear (Standard)
Linear forecasting follows the existing trend in the data and extends it forward in a straight line by the number of forecast units you select. It is the right choice when your workload grows at a steady, predictable pace — a transactional table adding a roughly consistent number of rows each week, for example.
Exponential (Aggressive)
Exponential forecasting assumes the rate of growth is itself increasing rather than staying flat. This tends to produce a more accurate forecast when growth is genuinely accelerating — a logging table growing faster as an application’s user base scales, or a reporting database expanding as more business units are onboarded. Per the SQL DM documentation: “If the rate of growth is not constant, the exponential forecast type gives a more accurate forecast of future growth.”
Linear vs Exponential Forecasting – Linear extends a steady trend; Exponential models accelerating growth.
Tip: Before committing to a single model, look at the shape of the historical trend. Applying Linear forecasting to a workload that is actually accelerating will consistently understate how soon you need to act. Running both a Linear and an Exponential forecast side by side and comparing is a useful sanity check.
The forecast reports require no dedicated configuration — but getting reliable results depends on a few things being in order before you run them.
Every forecast report reads from the disk, database, or table size history that SQL DM has collected continuously since monitoring began. If an instance was added recently, there may not be enough historical data yet for a reliable forecast. The general guidance from the documentation is clear: select the largest possible period of historical data and the shortest possible projection into the future for more accurate forecasting.
A forecast built on six months of history projecting three months forward will generally be more reliable than one built on two weeks of history projecting a year out. If you have recently added an instance, consider running a smaller, near-term forecast until more history accumulates.
Before selecting Linear or Exponential, spend a moment looking at the historical data in the report. A steady, consistent slope points to Linear. An accelerating curve points to Exponential. Using the wrong model does not break anything, but it will produce projections that diverge significantly from reality over longer time horizons.
Each report lets you filter by specific instances, databases, or tables. Running a Table Growth Forecast across every table on every database is possible, but the most actionable workflow is to start broad (disk volume), identify the specific scope that needs investigation, and then narrow down. This saves time and makes the output easier to act on.
A forecast run once is a snapshot. A forecast run monthly or quarterly is a planning tool. Compare each run against the actual growth since the last forecast to assess how well the model is tracking reality, and adjust your forecast horizon or type if it is consistently over- or under-estimating.
The following steps walk you through running all three forecast reports from within SQL Diagnostic Manager. You can run each report independently, or follow the full drill-down workflow from disk to database to table.
▶ Watch the Tutorial First
IDERA’s Capacity Planning with SQL Diagnostic Manager tutorial walks through the complete workflow inside the product — from opening the Plan reports to reading a forecast result. If you are setting these up for the first time, watching the video first (about 5 minutes) gives you a clear picture of what the interface looks like before you follow the written steps below.
Watch on YouTube: https://www.youtube.com/watch?v=K8qqmt6rlkg
SQL Diagnostic Manager Reports panel — Plan reports contains all three forecast reports
Use this report to project future disk space needs based on current and historical growth rate trends across the volumes hosting your monitored SQL Server instances.
Database Growth Forecast — sort by projected growth to quickly surface which databases need attention
Note: The Disk Space Usage Forecast report does not display the maximum capacity of the disk. It projects usage growth but does not calculate a specific “runs out on this date” value. Use it to estimate how much space you will need, then cross-reference with the actual volume capacity in your infrastructure tooling.
After identifying volumes with concerning growth trends, run the Database Growth Forecast to determine which databases on those instances are responsible.
Once you have identified which databases are driving growth, use the Table Growth Forecast to pinpoint the specific tables responsible — and decide whether the growth reflects expected usage or something that needs attention.
Running these reports once is useful. Running them on a recurring schedule turns capacity planning from a reactive fire drill into a proactive, predictable process.
| Task | Report to Use | Where to Find It |
| Project future disk space needs across volumes | Disk Space Usage Forecast | Reports > Plan |
| Identify fastest-growing databases | Database Growth Forecast | Reports > Plan |
| Find which tables are driving database growth | Table Growth Forecast | Reports > Plan |
| Use for steady, consistent growth rates | Any report — choose Linear | Forecast Type selector |
| Use for accelerating or variable growth rates | Any report — choose Exponential | Forecast Type selector |
| Maximize forecast accuracy | Any report — largest history, shortest horizon | Historical & Forecast period selectors |
Full documentation for these reports is available in the SQL Diagnostic Manager wiki:
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