Description

The MX960 fan tray identification in the logs and inventory varies. This article provides a mapping of the references.

Symptoms

On a MX960 chassis there two fan trays identified in show chassis hardware .

Example: 
Fan Tray 0       REV 05   740-014971   <snip>            Fan Tray
Fan Tray 1       REV 05   740-014971   <snip>            Fan Tray

In the logs or alarms, the messages regarding fan trays refer to top or bottom fan tray: 

MX960> show chassis alarms | no-more
3 alarms currently active
Alarm time               Class  Description
2018-06-15 03:46:38 UTC  Minor  Bottom Fan Tray Pred Fail
2018-06-15 03:46:38 UTC  Major  Bottom Fan Tray Failure

Which tray number is the bottom fan tray?

Solution

Fan Tray 0 is the Upper Fan Tray.
Fan Tray 1 is the Bottom Fan Tray.