# Health Trend

Health Trend displays the health history of a subnet in an area chart.

The card shown in the previous figure displays the health history of a subnet in an area chart. On the chart is the current health score which is calculated with the following equation:

where:

- Sj = the score for attribute j

- Wj = the weight for attribute j

The score for an attribute can be calculated using the following formula:

where:

- Vj = the current value for attribute j

- Bj = the current baseline for attribute j

Currently, the attributes, their source and their weight in the formula are as follows:

Attribute | Source | Weight
--- | --- | ---
Number of switches | ImageInfo | Average number of active ports per switch + 1
Number of HFIs | ImageInfo, FabricInfo | Average number of active ports per HFI + 1
Number of Inter Switch Links | FabricInfo | 3
Number of HFI links | FabricInfo | 2
Number of Active Ports | ImageInfo | 1
Number of Non-degraded Inter Switch Links | FabricInfo | 3
Number of Non-degraded HFI links | FabricInfo | 2

Weights represent the relative importance of one attribute against the others. For example, consider the small fabric in the following image: two 48-port switches connected by four ISLs and serving eight nodes. In this configuration, a switch down will have 5 times more impact in the health score than a HFI link down (switch weight = 4 node-ports + 4 ISLs + port 0 + 1 = 10 against weight HFI link = 2). However, the impact is even greater if you consider that a switch down may also affect other attributes. In this example, the health score goes down to 53% when you bring down one of the switches but only goes down to 93% when you bring down a HFI link. The end result is that even small changes in the fabric configuration are not diluted when the size of the fabric is big: in simulations with a fabric of over 8K nodes, a port being brought down is reflected with the non-perfect score of 99%.

Health Score Example

You can see the current values of each attribute and their baselines by hovering the mouse over the score; a tooltip appears to help you determine the source of a non-perfect score. The baseline values for each attribute are taken during initialization of the application and whenever the number of switches or HFIs increases in the fabric.