keeping your cabinet clean (was Re: Looking for help @ 60 Hudson)

Dovid Bender dovid at
Thu Nov 16 17:13:58 UTC 2017


Thanks for the in depth response. My biggest problem is that the DC gave us
cabinets on the smaller side which makes them almost impossible to work
with. If I was building out fresh I would prob get a cage and build out
with big cabs but my boss isn't offering such luxuries.....

On Mon, Nov 13, 2017 at 8:04 PM, Ken Chase <math at> wrote:

> Some tricks I've learned managing multicustomer/shared cabinets over the
> last
> 20+ years...sorry it's long, but I think there's some good info on keeping
> things clean and maintaining sanity. Please send your protips.
> Most of this is lower-end 1-4U sized mixes of gear specific and specific to
> cabinets that have 2-6U+ flux per quarter with some rushed installs. Huge
> one-time 12U blade installs of $1M appliances usually lend to gorgeous
> cable
> management schemes (and proper budgets) being included. No such lux here!
> TL;DR: thin premade ethernet of exact lengths and multiple random colours
>   (never black!), use min gauge required power cable thickness of exact
>   length, face A/B PDU's backwards on one side of rack cable management on
>   other side, never get less than 30" wide x 36" deep cabinet (if not,
> wider
>   better than deeper), premeasure vert mount rail positions to be
> compatible
>   with rail length/ front of server clearance, prewire front of rack
>   power/ether if needed (leave string too), practice tooless rail removal
>   while you can still get in above/below, rack similar-depth gear together,
>   switches face backwards (with front-to-back airflow switch config option
> of
>   course) on rail-shelves not ears (that bend over time anyway) so they
> can be
>   extracted out front and easily replaced in emergency.
> Details:
> Installing in 30" wide x 36" long cabinets makes all the diff over 24" x
> 30".
> A/B 0U PDUs on one side, cable wrangling ladders on other.  More room =
> more
> flexbility. (If have no side panels and no neighbours, 24x30" is ok). 36"
> deep
> allows facing the PDUs backwards not sideways - cableheads extend
> backwards,
> not into the rail-tail path/airflow/etc. Worth getting the
> 90degree-bent-head
> cables too if you need the spare inches. (I ofset my PDUs vertically by
> 1/2 a
> plug-spacing distance so cable from left one fits between cableheads of
> right
> one.)
> Avoid racks that don't use cagenuts. Prethreaded holes get abused and
> stripped. Try to get the right size of cagenut, there's a few standards out
> there. Some will fit - poorly. (Either they fall out under weight or you
> end
> up trying to force them in with a thin screwdriver - I've seen people stab
> themselves in the hand. Ask for a cagenut tool (J-hooked shaped piece of
> metal that
> looks like a bent desktop-case PCI slot cover.)
> Having many power cables of varying lengths is key (but why doesnt anyone
> make
> 15" and 21" power cables?). Not having ziptied loops of 12ga wire hanging
> around made things much nicer (and better airflow).  More $ but worth
> sanity.
> Esp. with varied coloured heads. Great for tracing (see ethernet below).
> Wire
> the gauge required - I find 10ga (6' long..) wire delivered with 100VA-max
> server
> configs often. Too thick to manage properly and usually unnecessary. But
> check
> your warranties and theoretical max power envelopes.
> Yes, full rack solns w/extendible arms exist but generally require vendor
> compatibility. Expensive too. Great for one time well-funded installs. Not
> practical for varied species installed over longer periods.
> Prewire any front-of-rack-powered gear when you first get the rack. I have
> 5
> pairs (A/B) going to the front permanently ziptied and labelled - 3x2 in
> use
> for my back-facing switches, 1 for a small piece of gear (low watt
> microtik),
> others spare.  Also prewire some proper length (multiple colours of) ether.
> Fishing ether through the side can be impossible in a full cabinet in a
> dense
> row (we're in APC pods). I leave string in there too (probably will use it
> for a twinax pull to the microtik soon, and pull more string with).
> Curse vendors for not picking a standard side (left vs right) for power
> ingress!
> (ibm and dell vs supermicro, sun and hp, IIRC?)
> Beware Dell's long fins/tails on their rails - won't fit in a 30" cabinet
> if
> your vert mount rails are too far back - or it blocks the power cord head
> on
> the pdu if it faces sideways/etc. And beware max/min rail extension - Dell
> seems 'longest', with many min. rail lengths of 25.5". I think I saw min.
> 26.5" once.
> Also had a cx jam a long Dell rail's tail into his fully assigned cabinet
> - in
> between a powercable head and the pdu body it was plugged into.  BZZT!
> Took 20
> min to get a monkey to reset at central panel. Thank proper cabinet
> grounding
> cables, right?)
> If you have an entirely empty cabinet to start with, grab a few different
> rails and ensure your cab's vertical mount rails are all within spacing
> spec.
> and give door-closing clearance to server noses. (See reference tables.)
> Moving them later can be impossible (though with sunfire rails that slid to
> varying lengths, it worked out luckily!)
> Must admit Dell's tooless rail installs are awesome now. Better than
> supermicro's and sun's (Sunfires). Learn how to derack them before you
> install, and practice a few times while you can still get your
> fingers/tools
> in from above/below. Make notes on how it works. Trying to guess how to
> derack
> a single U rail sandwiched in with no other access can be nearly
> impossible,
> especially an old EOL one with no identifying marks to google.
> Try to rack similar depth gear together. Nothing like having 1U 27" long
> Intels sandwiching 1U of 3/4 depth supermicro between them - cant get your
> hands in to do anything. 2U minimum together, but 3+ is better. Stash a
> headlamp
> in the rack too to see into these wells.
> Having more switchports than necessary (3 redundant 48 port switches with
> avg
> 2xc/box, avg 1.5U per box, 42U cabinet) allows 4' ethernet cables to be
> put in at
> exactly 3.75' extension into a switchport - minimal extra slack, just
> enough
> to manage the cable and keep it unstressed.  Folding spare cable into
> management ladders makes manual tracing hard, and is bad form. Crimping
> your
> own rj45 ends for exact lengths is risky. Done it many times (and once saw
> a tech do
> it before a bgp session timed out on a damaged live cable! :), but results
> are
> poorer than factory crimps and dont resist stress well. ('Sides, do you
> have 8
> different colour spools? See below.)
> Switch racking - I'd rather them on shelves not ears - then you can pull
> out
> your backwards-facing switch ass-first from front of the cabinet and slide
> the
> replacement in without moving cables too far -- trying to get the ears past
> the cabling can be heinous (and most ears cause major cantilevering due to
> deep heavy switches - after a few years I find things are bent from weight,
> impinging on the U below). There are thin little 3" wide rail-edge
> 'shelves'
> you can get, but your switch may not give the spare vertical mm required
> (about 3-4mm) - works best with 2u+ sized gear where there's spare mm play.
> Proper cable management trays/guides between the switches is great too
> (though
> eats U). Your density/financials will determine if that's viable. Its worth
> the U/sanity usually.
> Out of U for cable mgmt but have spare depth? Bungee cords won't work as
> anchor points to ziptie too - they sag in the heat over time. But rubber
> bungees ('tarp straps') work great.
> Though not for full 100m ether lengths, narrow gauge ethernet is key.  You
> can
> fit like 8-12 of them into a run of what 4-5 took previously. I've had zero
> issues with them with rack-lengths of cable. Worth the $.
> I wish there was thin bicolour ethernet - it's sexy to have all your ether
> coloured the same (or same per category - red mgmt, yellow public, white
> internal) -- but then you need to know where the failed port 34 cable is...
> tracing identically coloured cables can suck, your eyes start playing
> tricks
> looking at 30 cables in a twisting bundle that you ziptied too tight
> trying to
> be pretty - and under tension, yanking on them may not identify the right
> cable properly -- even with labels (you stop trusting them anyway after the
> first couple errors or when job security is thin).
> I tend to use as many random colours as possible -- and note it in the
> switch
> configs. If the switch config doesnt match, slow down and check things
> twice
> from scratch. (Keep many colours and lengths handy for new installs! Blue
> is so
> ugly - peach ftw, amirite?).
> Note that no pattern of colour use will work - wire all mgmt ports as one
> colour,
> or all ports of one server one colour - either way, you assume the colour
> means
> the cable is wired a certain way, and that leads to errors. With no
> pattern,
> no dangerous assumptions are made - must check with the switch config.
> Maxing out
> #s of different colours leads to easier identification/fewer chances of
> neighbouring
> cables of same colour.
> If the management layer of your company doenst have to slave over racks,
> this
> is likely not an option. They like the pretty and impractical stuff best
> of course.
> Labelling only works so well - in 100-120F exhaust paths most glue just
> melts
> off. One client I had no input on the install for has 100s of little
> silvery
> labels littering the floor/lower U of their cabinet. So pretty! And goey
> cables. And thank god they're all white! Makes tracing so easy! :P
> (Of course no one ever wires black ethernet, right? That's a capital
> offence!)
> /kc
> On Mon, Nov 13, 2017 at 05:05:35PM -0500, Chuck Anderson said:
>   >On Mon, Nov 13, 2017 at 01:30:25PM -0800, Seth Mattinen wrote:
>   >> On 11/13/17 12:49, Mike Hammett wrote:
>   >> >Keep the humans out of the rack and you should be fine.
>   >> >
>   >> >Where should I send the invoice?:-P
>   >>
>   >>
>   >> It's easy to keep a rack nice if you take the time. I've spent hours
>   >> removing and replacing cables in neatly dressed bundles because
>   >> equipment changes required a different length/type cable, but
>   >> sometimes that's what you gotta do to keep things neat and tidy.
>   >
>   >Exactly.  Most people do not want to spend the time to do it properly.
> --
> Ken Chase - math at Guelph Canada

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