Fabric Expansion Calculator
Check whether new leaves fit the existing spines, and count the spine ports, cables and bandwidth they add.
Inputs
Fabric Bandwidth Added
6,400Gbps
Leaves after Expansion
24
Spare Ports Left on Each Spine
16
Maximum Leaves These Spines Support
32
New Fabric Cables Required
64
Fits Without Adding Spines
Yes
Step by step
Values used
Leaves today = 16 switches; Leaves being added = 8 switches; Spine switches = 4 switches; Uplinks from each leaf to each spine = 2 links; Fabric ports available per spine = 64 ports; Uplink speed = 100 Gbps
Fabric Expansion
ports used per spine = total leaves × uplinks per spine; added bandwidth = new leaves × spines × uplinks per spine × uplink speed.
Fabric Bandwidth Added
= 6,400 Gbps
Leaves after Expansion
= 24
Spare Ports Left on Each Spine
= 16
Maximum Leaves These Spines Support
= 32
New Fabric Cables Required
= 64
Fits Without Adding Spines
= Yes
How it works
Each new leaf consumes one port on every spine for each parallel uplink, so spine port count — not rack space — is what caps a two-tier fabric. When it runs out the options are a super-spine tier, fewer uplinks per leaf, or faster uplinks. Discovering the spines are full during a build weekend is the classic data-centre stall; this is the arithmetic that should be done at design review.
Formula
Fabric Expansion
ports used per spine = total leaves × uplinks per spine; added bandwidth = new leaves × spines × uplinks per spine × uplink speed.
- uplinks per spine
- Parallel links between one leaf and one spine
- maximum leaves
- Spine fabric ports divided by uplinks per spine
Frequently Asked Questions
How is Fabric Expansion calculated?
ports used per spine = total leaves × uplinks per spine; added bandwidth = new leaves × spines × uplinks per spine × uplink speed. Each new leaf consumes one port on every spine for each parallel uplink, so spine port count — not rack space — is what caps a two-tier fabric. When it runs out the options are a super-spine tier, fewer uplinks per leaf, or faster uplinks.
Why does Fabric Expansion matter?
Discovering the spines are full during a build weekend is the classic data-centre stall; this is the arithmetic that should be done at design review.
What values do I need to enter?
This calculator takes 6 inputs: Leaves today, Leaves being added, Spine switches, Uplinks from each leaf to each spine, Fabric ports available per spine, Uplink speed. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.