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
