I am doing a core switch refresh, going from a 3750X stack to a pair of N3ks. A few details:
I plan on leaving the stack as L2 access layer for PC clients.
I am migrating the Blade Center and SAN to the Nexus 3Ks, hoping to use vPC.
The blade center and SAN are on different VLANs and therefore connected via L3.
My plan is to setup the N3ks alongside the stack and uplink them, then migrate a few L2 links from the Blade Center and SAN to the N3ks, then shutdown the SVIs on the stack and enable them on the N3Ks.
My concern is that this will cause loss of connectivity and I will require a huge outage window. Do I have any options to make this happen without loss of connectivity? Someone mentioned to me HSRP but then when I have to remove that config I'll still need an outage window.
I think you have the correct approach by building the N3ks in parallel to the 3750x switches and slowly migrating from the 3750 to Nexus. If you do all your planning and testing a head of time, your downtime will be limited to the amount time it takes to shutdown the SVIs on the 3750 and bring them on line on the Nexus. This approach should not require a long outage window.