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Short version of question:

Is there any reason a UPS (or any other device) should be at a particular level in a rack.

Long version (with explanation):

I have a full height rack with two servers, two Dell rail mount UPS units, a direct attached storage device, a tape drive, and some other items.

I want to reorder the items vertically. Is there any reason a UPS (or any other item for that matter) has to or should be at a certain position? The UPS is currently at the bottom, but I'm assuming this is just accidental.

The motivation for the re-ordering is that there's a mess of wires back there, but more importantly the two bottom items (UPS and Powervault) are much less deep then the items on top of them. As a result the cables that attach to the back of these items are almost impossible to reach.

I suspect the fact that I have this problem at all suggests that I'm doing something wrong.

I'd appreciate any info about:

  1. Whether there's any reason to have a UPS or any other device at a particular vertical level within a rack.
  2. Good tips and tricks for managing the mess of wires behind the rack. Some devices I have have cable arms but those seem to do more harm than good (wires "catch" when arm is being extended for some reason).

Thanks!

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Extra Info: This is a dell rack with mainly dell servers/components. –  user426724 Aug 31 '11 at 20:42
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4 Answers

up vote 18 down vote accepted

It is probably not place at the bottom accidentally. Typically the UPS is the heaviest thing in the rack. Meaning it is easiest to install it at the bottom where you don't have to lift it up.

One might argue, that putting the heaviest things at the bottom should also make it more stable. If it was top-heavy, and not bolted down, then there is the remote possibility a strong earth quack would tip your rack.

Good tips and tricks for managing the mess of wires behind the rack.

Lots of cable management

Some devices I have have cable arms

IMHO the cable arms that come with the 1U servers mostly cause more harm then good. Disconnecting, and completely removing the 1U boxes usually seems easier to me. But I really like them on the 6U SAN. The drives must be replaced from the top, completely removing that would be a PITA.

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OMG earth quack! –  Dave Costa Sep 5 '11 at 17:47
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All rack-mounted devices are shielded and can tolerate being next to any other device designed to go inside the rack. So, yes... you can put the UPS at the very-tippy-top... and put everything else at the bottom... but my experience is that UPSes are HEEEAAVVVVY... and it's just easier to stick 'em at the bottom.

As far as good cable-management goes... most rack-enclosure setups have unique bits that work best with the manufacturer's configuration. (i.e. Dell servers + dell rack + dell cable management = WIN... but adding Supermicro servers + HP rack + random cable management = nightmare) It's always best to stick with the brand equipment you're using... but there are some pretty OK generic options. They're just not quite as elegant as all single-brand.

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Good tips and tricks for managing the mess of wires behind the rack.

If your systems are mostly plugged into the UPS, consider using a PDU (Otherwise called a 'power-strip', but better quality then the power-strip you have at home or on your workbench) instead of plugging directly into the UPS.

A good PDU can help with both the the cable-management problem and the UPS placement problem. Leave the UPS at the bottom, plug one or two PDUs into the UPS (This is usually only happens once) then plug systems into the PDU.

Vertical PDUs and short power cables can be very good ways to cut down on power cable clutter.

Horizontal PDUs are much lighter then a UPS, and can be placed in the middle or at the top of the rack.

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I have one vertical PDU. Unfortunately the issue is that I have two UPS (neither is enough to handle load of all devices). As a result, a few devices plug directly into auxiliary UPS, which drives me crazy. I'm not sure rack has space for an additional vertical PDU. I'll look into a horizantle one/what my general options are. Thanks! –  user426724 Sep 1 '11 at 18:05
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Whether there's any reason to have a UPS or any other device at a particular vertical level within a rack.

If you have a KVM make sure that it's either at sitting or standing level. I usually go for standing level as most KVM operations are quick. I once had to work at an installation where they didn't consider KVM placement and had it near the top of the rack requiring a stepstool to access.

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