During a discussion recently with some other UCS-savvy folks, I realized that there may be some confusion in how to place mezzanine adapters in full width blades when you’re only using one adapter.
First, a quick review of how UCS pins mezzanine ports to uplinks. I’ll skip the one uplink option, since all ports use the single uplink.
In a two-uplink configuration, all odd numbered slots use uplink #1, while all even numbered slots use uplink #2. (Easy to remember – odds go to the odd uplink, evens go to the even uplnk). Since a full-width blade occupies two horizontally adjacent slots, each full width blade will contain both an even and an odd numbered mezzanine slot. Let’s look at the slot numbering – this diagram shows half width blades.
Consider the case of 4 full width blades, all with a single mezzanine card in the “left” (as viewed from the front) slot. In a two-uplink configuration, only the first uplink would be used – since all odd numbered slots are pinned to uplink #1. Uplink #2 would be completely unused.
In a four uplink configuration, the pinning is as follows:
Ports 1,5 -> Uplink 1
Ports 2,6 -> Uplink 2
Ports 3,7 -> Uplink 3
Ports 4,8 -> Uplink 4
Consider the same previous example. In the four-uplink configuration, only uplinks 1 and 3 are used, as these are the uplinks pinned to the odd-numbered mezzanine slots. Uplinks 2 and 4 would remain idle.
When using full width blades and single mezzanine cards, it’s important to consider the other blades in the chassis when selecting where to install the mezzanine card. Individual configurations will vary, depending on the number of half and full width blades in use.
If using all full width blades with single mezzanine cards, two of the blades should have the mezzanine card in the left slot and two blades should have the mezzanine card in the right slot. By properly selecting the mezzanine placement, such as first blade (slots 1 and 2) in the left (1) position, the second blade (slots 3 and 4) in the left (3) position, third blade (slots 5 and 6) in the right (6) position, and the fourth blade (slots 7 and 8) in the right (8) position, you achieve proper usage of all four uplinks. The inverse is also functionally identical, populating mezzanine slots 2, 4, 5, 7.
For a two-uplink configuration, any combination of mezzanine layout is acceptable as long as two blades have mezzanine cards in the left slots, and two have mezzanine cards in the right slots. If beginning with a two-uplink configuration, it would be wise to use the four-uplink layout to minimize future reconfiguration if expanding to four uplinks.