Comments on: Chassis Discovery Policies in UCS

By: Some UCS Links - blog.scottlowe.org - The weblog of an IT pro specializing in virtualization, storage, and servers

Wed, 18 Aug 2010 14:11:22 +0000

[...] UCS Server Pools: Use Cases Placement of mezzanine adapters in full width blades Chassis Discovery Policies in UCS Cisco UCS Server Pools: Configuration Why Cisco UCS is my ‘A-Game’ Server Architecture [...]

By: Brad Hedlund

Brad Hedlund — Mon, 21 Jun 2010 12:23:43 +0000

Dave,
In either case, by setting policy to 2 or 4 links, you’ll never have a chassis online with just 1 link bacause someone forgot to click “Re-ack”. Worth a 5 second investment of your time? I think so.

By: Dave Alexander

Dave Alexander — Mon, 21 Jun 2010 11:38:11 +0000

Brad -

The policy makes the assumption that all chassis will be configured equally, or at least that some minimum number of links is acceptable. If I have a mixed configuration of 2 and 4 link systems, then I’m right back to the “risk” of putting a system into production with only 2 links when perhaps I expected 4. Or if I set my policy at 4 links, I have to re-ack the 2 link systems to make them functional. In either example, one of the chassis is going to require a re-ack to make them function as expected.

My whole point is not that the chassis discovery policy doesn’t do anything, it’s just that it seems to be providing a very small benefit and creates more confusion (as evidenced here) than it’s worth.

By: Brad Hedlund

Brad Hedlund — Mon, 21 Jun 2010 04:08:16 +0000

Aaron,
If you can’t trust the system’s ability to enforce a policy what are you doing with UCS in the first place? The entire system is policy driven.
It’s not about blindly adding chassis. It’s about reducing the potential for human error, and obtaining proper logging of the human error, should it occur.

By: Aaron Delp

Aaron Delp — Mon, 21 Jun 2010 03:46:19 +0000

Brad – In Joe’s example of setting to four as a personal best practice and then “re-ack” or what I have done in the past to just set to one (or two) and re-ack. Everyone here will follow’s Dave’s “enable ports, re-ack, check link status”. It’s the responsible thing to do. I just don’t believe many customers will blindly add chassis and trust the policy. I get your point here and I see the advantages to setting the policy in large environments but I’m in the same boat as Dave on this one.

By: Brad Hedlund

Brad Hedlund — Mon, 21 Jun 2010 03:26:55 +0000

Dave,
Your “process” relies upon someone correctly following it every time to avoid a chassis going into production with only 1 link. Simply setting the policy to 2 links would prevent the risk of human error. With a chassis discovery policy I can be assured a chassis never comes online with fewer than 2 links, for example, without relying on someone clicking “re-ack”. Its a simple insurance policy for the 5 seconds it takes to get it configured.

By: Dave Alexander

Dave Alexander — Mon, 21 Jun 2010 03:01:49 +0000

I guess my point is, like Joe, I’m not going to put a chassis into production without checking the status of the links. I’m not seeing any value in setting the discovery policy, when no matter what it’s set to a 1-click re-ack makes all links active. My process for adding a chassis is “enable ports, re-ack, check link status”. The chassis discovery policy isn’t valuable to me.

By: Brad Hedlund

Brad Hedlund — Mon, 21 Jun 2010 02:38:12 +0000

Aaron,
It appears to me Dave got this to work as desired. His description of the behavior in this article sounds right. If the policy didn’t match the number of links, the FEX did not come online until he “Re-acknowledged” the chassis, a manual intervention that basically acknowledges the chassis is out of policy. However if the policy matched the uplinks, the FEX comes online without a “Re-acknowledge”. Right?

By: Aaron Delp

Aaron Delp — Mon, 21 Jun 2010 02:20:52 +0000

BTW – Brad and Joe, I’m not doubting the intention of it and I think it would be a good idea. But, when I tested it (1.1 code if I remember right) it just didn’t seem to actually work. Has anybody gotten it to work as desired?

By: Aaron Delp

Aaron Delp — Mon, 21 Jun 2010 02:11:06 +0000

I did a BUNCH of testing of this setting it to 4, 2, and 1. I then went up and down with the number of uplinks. My conclusion was it was useless as well. You can absolutely bring up a chassis with 1 link with the policy set to 2 and the pinning will be for one uplink. I’ll dig up my notes (and screenshots that I took along the way) tomorrow if needed.