One of my readers sent me a lengthy email asking my opinion about his ideas for new data center design (yep, I pointed out there’s a service for that while replying to his email ;). He started with:
I have to design a DR solution for a large enterprise. They have two data centers connected via Fabric Path.
There’s a red flag right there…
While it’s definitely better to use Fabric Path (or Avaya’s SPB fabric, or Brocade’s Metro VCS Fabric) than the MLAG-over-WAN kludges, extending bridging across two data centers makes them a single failure domain, as some people found out the hard way.
Most of the applications run in a HA manner in both locations.
I wonder why people still think that’s a good idea. Loss of DCI link will probably just break every application running across both locations (if the application would be written correctly they wouldn’t need L2 extension anyway).
Services run in a HA manner - one service device is active in one location and standby in the other. They communicate via Layer 2.
Anyway, the reader’s idea was to replace Fabric Path with ACI:
According to Cisco and to your webinars ACI is a good candidate for a DR solution.
I don’t remember ever saying ACI is a good candidate for a DR solution ;), but it’s definitely the least horrible one. In fact, any solution that replaces bridging with host routing (ACI, DFA or Cumulus Linux redistribute ARP) is infinitely better than stretched VLANs because it removes the uncontrolled flooding behavior that’s the root cause of many catastrophic network failures.
Finally, as my reader was talking about disaster recovery I advised him to go back and talk about the real business needs. Once you get into that discussion, you often realize you don’t need stretched layer-2 fabrics, because the other infrastructure (example: storage) doesn’t support fully automated recovery.
Want to know more?
I’ll be running a Building Active-Active and Disaster Recovery Data Centers workshop during the Data Center Day (September 16th 2016) in Zurich, Switzerland… or you could watch the webinar, but if you’re like dozens of your colleagues that registered for my online course you know that the live stuff is always better than a recording, right?