data center wiring Q: om3 optic patch panels, good or bad?

[linux-works]

hope its ok to ask a computer networking/cabling question.  maybe some folks here have some real world experience in this; I can't find anything online that will answer the question.

at work, we are upgrading our racks to 10gbe (10gig ethernet).  the common standard is om3 fiber cables in aqua jackets.  they connect to SFP+ modules that are just tiny 'gbic-like' transceivers.

all that's well and good; but I am thinking of allowing users (lab users who need to do reconfigs) to move opto cables from one port to another, so they can get access to hardware-based traffic generators (like a high end spirent or ixia).  rather than having them wear out the sfp+ modules or the expensive spirent ports, I'd prefer they move short patch cables from one opto block to another on a 1U patch panel.

question is: how GOOD are those patch panels?  opto alignment is critical with multimode om3 style fiber and while I can find a 'mating cycle count' of 500 for those platic LC-LC style connectors, that does not tell me anything about how weak they will become as they start to see plug/unplug wear cycles.  the light may still get thru, but we may start to see subtle errors and not even realize it.

so, is this a good idea to consider - using a patch panel for LC-LC style connections?  or just avoid it entirely, don't have to worry about dB loss from connectors and junctions and small patch cables - and just replace the sfp+ modules if/when they wear out.

anyone have any real experience with om3 LC or even SC style fiber patch panels in a data closet or data center?  again, they will see several plug cycles as the lab guys reconfig their test setup each day.

[The Soulman]

Standard LC connectors are mechanically not very robust and I certainly wouldn't recommend to daily re-patch them.

This is a solution:

http://www.neutrik.com/en/data/opticalcon/

[linux-works]

thanks for the reply.

all I can find from a net.search is that the connector 'mating cycle' rating is 500 inserts.  if it was 50, I'd see your point, but 500 sounds like a lot.

have you personally seen connections fail due to plug/unplug cycles?

[Elf]

question is: how GOOD are those patch panels?  opto alignment is critical with multimode om3 style fiber and while I can find a 'mating cycle count' of 500 for those platic LC-LC style connectors, that does not tell me anything about how weak they will become as they start to see plug/unplug wear cycles.  the light may still get thru, but we may start to see subtle errors and not even realize it.

I would use a patch panel as a cheaper solution if only from a practical, operational perspective. Keep people away from the expensive equipment and logically abstract the wiring a bit. The plastic snap-in LC-LC connectors are also a lot cheaper to replace than 10GBASE-SR/SRM SFP+ modules. In over a decade of service provider engineering at datacenters (although no longer) I have never seen a patch panel actually wear out, but I should also say that datacenters typically don't have such frequent re-patching. Usually the failure mode for optical is fractured fiber.

Since this is the Internet and it's always fun to spend other people's money, I can also suggest the "premium" solution of an optical cross-connect switch, e.g. the Glimmerglass Intelligent Optical System series. Cable everything up and switch it from your desk. You can also do fun things like fan out the wavelength to multiple recipients.

I would also consider running singlemode. If you are already counting your dBs with multimode to worry about the patch panel and connectors, it is probably time to make the jump. I think the days of multimode are numbered with 100GigE and up, and with the right optics vendor, singlemode is not that much more.

[linux-works]

thanks for the reply.

I'm 100% onboard the idea of wearing out the patchpanel and patch cables instead of the expensive gear that is behind it.  there will be very expensive stuff that our engineers need to switch between; its a lab environment and we're testing/developing new stuff that is at the 10gig speed and faster.  om3 seems to be the main player, with om4 being the 100gbe preferred media.  this is for short cables; all inside one rack, never going farther than about half a rack, vertically.

some work can be done by playing vlan games in the backbone and access switches; but sometimes our guys want to bypass that and 'go direct' to ensure that no other stuff is in between.  in those cases, you really do have to allow people to move patch cables.

the sfp+ 'gbic thingies' have a much lower rated mating lifetime.  200 or so, or less.  and they plug into the 'expensive gear' so we want to leave that alone, as much as we can.  for this, I'm ruling out those DAC cable thingies.

I'm kind of new to this 10gbe and faster world   before I recommend that we go with some kind of patch panel, I would like to have more than 'a feeling' why I think its a good idea.  and I can't find anything online that really gives battle experience with this.  maybe that's a good thing, perhaps it means that they JustPlainWork(tm) and, if so, I'm happy to design them into our test racks.

[linux-works]

btw, how much (roughly) does that glimmerglass thing cost?  is it actually a physical pt-pt connection that is mechanically moved?  I get the impression its not converting to electrical and back again; its staying all optical.  and a 'slow' connect time sounds pretty mechanical to me..

[Elf]

Yes, all mechanical MEMS mirror switching of the optical path. Same light coming out of it as what went in, minus a few dB.

It has been a while since I priced one out; all I remember was five digits rather than six for a 96x96 unit.

Edit: This article explains the workings of the units.

[radar_macgyver]

DAC cables can be finicky at 10 Gb/s, not all vendors support longer DAC cable lengths. With the right vendor, you can find an SFP+ pair plus fiber patch cable for less. Plus, as far as I know, nobody makes a DAC cable patch panel.

I've had good luck so far with fiberstore (fs.com), they sell good quality SFP+ modules and fiber patch cables at unbelievably low prices. I haven't had any fail yet in our modest setup at work. I used those in combination with a patch panel from Panduit that has keystone jacks for either LC duplex or CAT6.

Also, as mentioned earlier, consider singlemode. Especially at fs.com prices, it's a nice way to future-proof your cabling.