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Active Directory Replication Calculator

Estimate AD replication traffic per cycle, site link utilisation and end-to-end convergence time.

About Active Directory Replication Calculator

The KCC builds a bidirectional ring within a site, so a change travels at most half the ring to reach every controller, one replication interval per hop. Traffic per cycle is the change volume in the window, compressed for inter-site links. Convergence time, not bandwidth, is usually the constraint: with a 15-minute interval and twelve controllers a password change can take an hour and a half to be visible everywhere.

Formulas

Active Directory Replication

bytes per cycle = changes per hour × interval ÷ 60 × bytes per object ÷ compression ratio.

changes per hour
Object modifications originating anywhere in the domain
bytes per object
Replicated attribute payload plus metadata
compression ratio
AD compresses inter-site replication roughly 6–8×

Ring topology convergence

convergence = ceil(DCs ÷ 2) × replication interval

DCs
Domain controllers in the replication ring
ceil(DCs ÷ 2)
Worst-case hop count around a bidirectional ring

Worked example

With the default values below, Active Directory Replication Calculator returns Worst-Case Convergence Time of 90. Change any input above and every figure here is recalculated in your browser.

Inputs used

Domain controllersminimum 1 DCs
12 DCs
Directory changes per hourminimum 0 changes/h
5,000 changes/h
Bytes per changed objectminimum 64 bytes
2,400 bytes
Replication intervalminimum 1 min
15 min
Site link bandwidthminimum 0.01 Mbit/s
10 Mbit/s
Inter-site compression ratioaccepts 1–20 ×
6 ×

Results

Worst-Case Convergence Time
90 min
Replication Bytes Per Cycle
488 KiB
Transfer Time Per Cycle
0.40 s
Site Link Utilisation
0.044%
Changes Per Cycle
1,250

Step by step

  1. 1Values used
  2. 2Active Directory Replication
  3. 3Ring topology convergence
  4. 4Worst-Case Convergence Time= 90 min
  5. 5Replication Bytes Per Cycle= 500,000
  6. 6Transfer Time Per Cycle= 0.40 s
  7. 7Site Link Utilisation= 0.044
  8. 8Changes Per Cycle= 1,250

Assumptions and limits

  • The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Active Directory Replication calculated?

bytes per cycle = changes per hour × interval ÷ 60 × bytes per object ÷ compression ratio. The KCC builds a bidirectional ring within a site, so a change travels at most half the ring to reach every controller, one replication interval per hop. Traffic per cycle is the change volume in the window, compressed for inter-site links.

Why does Active Directory Replication matter?

Convergence time, not bandwidth, is usually the constraint: with a 15-minute interval and twelve controllers a password change can take an hour and a half to be visible everywhere.

What values do I need to enter?

This calculator takes 6 inputs: Domain controllers, Directory changes per hour, Bytes per changed object, Replication interval, Site link bandwidth, Inter-site compression ratio. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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