FCoE/CNA Deployment w/ Nexus 5K, HP 580s, QLogic

daniel.onwude igevioya at gmail.com
Mon Feb 27 22:35:43 UTC 2012


Working on a similar design and now know what to avoid :)

On Feb 27, 2012, at 4:22 PM, David Swafford wrote:

> Hi Everyone!
> I had several requests for more feedback on our FCoE experience, based on
> my comments from a thread last week, so I'm writing here with a bit more
> background on our project in hopes that it saves some pain for others :-).
> I'm with a sizable health insurance provider in the mid-west, and we've
> typically focused on technology vs. headcount as an overal strategy.  Based
> on that, we upgrade much more often than some of our peers in the industry
> because techology is still cheaper than long-term staffing costs.
> Last fall, we were faced with an issue of both power and rack capacity
> constraints in our primary datacenter, which is just three years old now.
> As various ideas were on the table, which included taking out a section of
> IT cubes to expand the DC, the most appealing idea was to consolidate our
> server and network infrastructure into what was coined our "High Density
> Row".
> We transitioned from Cat6500s as access to a Nexus 5K deployment, using 5Ks
> as both distribution and access for the new HD row.  We didn't like how
> oversubscription is handled on 2K FEXs when it comes to 10G links, so for
> the situation here all 5Ks made the most sense.  Our capacity needs
> couldn't justify 7Ks and while they would have been cool to have, we didn't
> want to blow money just because.
> Our SAN is an EMC Symmetrix with Cisco MDS switches in between it and the
> hosts (Fiber Channel).  In the new row, we deployed all hosts with CNAs
> (converged net adapters), which combine both FCoE storage and network in a
> single 10Gb connection.  Since FCoE was new to all of us, we use a phased
> approach that the Nexus offered where we brough straight fiber channel
> connections into our distibution layer 5Ks and used the Nexus' FCoE proxy
> functionality to convert between true FC to FCoE.
> From the host perpsective, it was only aware of FCoE connectivity to the
> Nexus.  VSANs had to be created on the Nexus to map back to the FC VSANs on
> the MDS side, Virtual Fiber Channel (VFC) interfaces were created on the
> Nexus side, and a few other settings had to be configured.
> Overall though, the config wasn't huge, but the biggest hurdle for was that
> as the network guys, we had to learn the storage side to be able to
> properly set this up.  So new terms like WWN (world wide name), floggy
> database, VSAN (a VLAN for storage), etc.  Also, on the Nexus side, you
> have to enable the feature of FCOE, as Nexus OS is very modulular and
> leaves most options disabled during the initial setup.
> The painful part, which is probably what might be of most interest here, is
> that we hit a very strange and catrastrophic issue specific to QLogic's
> 8242 Copper-based (twinax) CNA adapter.  As part of the burn-in testing, we
> were working with our server team to simulate the loss of a
> link/card/switch (all hosts were dual-connected with dual-CNAs to separate
> 5Ks).  We were using the Cisco branded twinax cabling and QLogic's 8242
> card (brand new HP DL580s in this case, new card, new 5K, new cabling).
> When a single link was dropped/diconnected PHYSICALLY (a shut/no shut is
> not the same here), the host's throughput on BOTH storage and network went
> to crap.
> Our baseline was showing nearly 400MB/s on storage (raw disk IO) tests
> prior to a link drop and  1-8 MB/s after!  This siutation would not recover
> until you fully rebooted/power cycled the server.  We had the same results
> accross every HP DL 580 tested, which was 5-6 of them I belive.  We
> replaced CNAs, cables, and even moved ports across 5Ks.  It didn't matter
> which cable, 5K, port, of card we used, all reacted the same!  The hosts
> were all Windows 2008 Datacenter, simliar hardware, Nexus 5K on current
> code, twinax cabling.
> This situation led to a sev 2 w/ Cisco, the equivalant w/ HP, EMC, and
> QLogic.  We used both the straight QLogic 8242 and the HP OEM'd version and
> the results were identical.  QLogic acknowledged the issue but could not
> resolve it due not being able to grab a hardware level trace of the
> connection (required some type of test equipment that they couldn't provide
> and we didn't have).
> As part of our trail/error testing, we had our re-seller ship us the fiber
> versions of the same QLogic cards, becuase we eventually got down to a gut
> instinct of this being a copper/electrical anomoly.  That instict was
> dead-on.  Switching to the fiber versions, with fiber SFPs on the 5K side
> resolved the situation entirely.  We are now able to drop a link with NO
> noticable degradation, back and forth, and eveyrthing is consistent again.
> We originally went the twinax route because it was signifiantly cheaper
> than the fiber, but in retrospect, as a whole, the danger posed was not
> worth it.  You might ask, well... why would you intentially drop the
> cable?  Think about a situation of doing a code upgrade on the 5K, since
> it's not a dual-sup box, you physcailly go through a reboot to upgrade it.
> That reboot right htere would have hosed our entire environment (keep in
> mind, the HD row's intent was to replace a signifiant portion of our
> production environment).  You could also have a HW failure on a 5K.  It
> kind of defeats the point of all this redundancy if your throuhput goes to
> hell when loosing a single path.  As our storage guys best put it "i'd
> rather loose a path than have bad performance through it....based on how
> things alert, I'd know right away if a path were down, but not if it were
> severaly degraded."
> Btw, we've been rock solid on the fiber-connected CNAs ever since.  We're
> still using copper on our connections to HP blade chassis though, which go
> to FLEX Fabric cards, as we couldn't produce the problem on those.  For
> those wondering, we did rebuild several of the DL580s from scratch (all of
> this was a new deployment, thankfully!), we also went through many
> iterations of driver updates/changes/etc.
> Lots of head-banging and teamwork eventually got us squared away!  This
> situation is a good example of why network guys NEED to have a great
> relationship with both server and storage guys (we're all really close
> where I'm at).  Had there been tension/etc between the teams, this would
> have been signifiantky harder to resolve.
> Hope this helps, sorry for the long winded email :-), but I think those
> interested will find it beneficial.
> David.

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