Cisco UCS QoS and boot from iSCSI

[#1]

Hello,

I recently installed a UCS Mini with a direct-attached CS235 and configured the blades to boot from iSCSI.  All was well with the initial ESXi installation until I received the attached error upon first boot to the LUN.  Nimble Support was great and they only changed my iSCSI QoS settings from using Gold to Best Effort to get ESXi to see the Nimble volume as a proper boot LUN.  Why is this the case regarding QoS?  In addition, I am using jumbo frames and I was able to get everything to work with the Gold class when using standard 1500 byte frames.

Thanks,

Mike

[javirodz75]

Did you fix this? Did you setup the Network Control Policy option "Action on uplink Fail" to Warning?

Let us know , thanks

[#3]

No, I wasnt able to understand why the Gold QoS class didn't work with jumbo frames when booting blades from iSCSI.  But changing to Best Effort as Nimble Support suggested seemed to work fine. Since it was a greenfield, I just went with it.  The only reason Nimble Support shared was that Nimble engineering said it was a "best practice." BTW, that is not a good explanation. Thanks for making it work, but I'd like to understand more.

[stooie2950]

Hello,

I have seen this also and I believe that you need to set best effort to 9216 as this is the class the return traffic comes back with. If it is not set then return traffic will come back at 1500 by default and if you going out with 9000 you will see all sorts of problems. Here is a support forum that I used.

https://supportforums.cisco.com/discussion/12027506/ucs-iscsi-boot-jumb-mtu

[#5 · Accepted solution]

Thanks for the reply. The frame size used was 9216. The only difference was the class.

While this particular implementation was boot from SAN, I just implemented a Nimble to an existing UCS, no boot from SAN, and I used the existing Gold class already identified for iSCSI. No issues there.