rackmount managed PDUs

Joe Greco jgreco at ns.sol.net
Thu Sep 25 14:21:10 CDT 2008


> Justin M. Streiner wrote:
> > I have some Tripp Lite PDUMH30NETs that work well and are reasonably 
> > priced, but they have a few quirks (no RS-232 console port, web 
> > interface seems to be a little shaky with Firefox, etc) that would 
> > become more annoying when scaled up to several rows of new rack 
> > footprints.  I'm also open to using managed vertically mounted PDUs.  
> > The plan is for each footprint to have "A" and B" feeds, so two 
> > PDUMH30NETs would take up 4U per footprint, which is a bit much...

I'll second the vote for APC, they make a flexible variety of products
that all "feel" the same, but support widely varying configurations.

> One thing to be aware of with the vertical PDUs is where they get 
> mounted.  A number of vertical Emerson PDUs were purchased for our DC. 
> However only one of the Liebert cabinets was purchased with the 6" 
> extension on the rear.  The PDUs mount on each side of the cabinet door 
> frame with the receptacles facing the opposing PDU.  Ie, both PDUs face 
> inward towards each other, not towards the front or rear of the cabinet. 
>   They stick out about 2" plus the power cords stick out at least 
> another 2", more depending on how hard you fight to force the power 
> cables into bundles and wire-tie them off to the frame.  The rails of 
> the servers barely clear the PDUs.  The cabling on the back of the 
> servers is made all the harder by the bundle of power cables in the way. 
>   It's a difficult physical problem to work around. 

We've used a very successful similar configuration where an extra set of 
vertical mounting rails is used at the very back of the rack *just* for 
purposes of mounting the 0U strips.  Most people usually dismiss this sort
of configuration as impractical due to the increased difficulty of 
accessing rack screws for the backs of the servers.  We have a "long bit" 
that we use with our power screwdrivers, it's 21" long and basically 
slides thru right behind the 0U strip.

Rack ends up looking something like this, from-the-top view:

http://www.sol.net/tmp/nanog/rack.gif

Extra set of vertical rails (vertical rails in red) in the rear.  To them
is attached, up to two per side, 0U PDU's.  Outlets face each other, which
is not *great* from an airflow reduction point of view.  We use cable
lacing strips (blue) in between the rear rail sets.  We're a velcro shop
and this works out pretty well for us.

For those times you need to get at the screws in the first rear set of
rails that are holding a server, you can stick your "long bit" or an
offset screwdriver in, because of course the set of rails holding the
PDU's is square holed, and the only holes obstructed are the ones holding
the 0U PDU's.

The main advantage of this over the quoted suggestion would be that it
sounds like the quoted suggestion is a hard mount to the rack, which
probably obstructs screw access, and may only allow one strip per side,
depending.  Of course, all of this makes various assumptions about the
available geometries.

... JG
-- 
Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.




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