vertical cable-management options.Keeping cables neatly organized within and between racksis vital for being able to work efficiently without disturb- ing other equipment.Cleaning up a rat’s nest of cablesis painful and cannot be done without taking equipment down.If you don’t provide reasonable ca- blemanagement, people will wire equipmentin all sorts ofinteresting ways, and you will later discover that you can’t take a piece of equipment out of the rack to replace broken hardware without bringing down three other critical pieces of equipment that have nothing to do with themachine you are trying to work on.
Horizontal cablemanagement usually screwsinto themounting rails and can be open or closed.Open cablemanagement has a series of large split hoops that all the cables go behind.Cables are slotted through the gapsin the hoops as they are run fromone place to the other.The hoops keep the cables within a confined channel or area.Closed cablemanagement consists of a channel with a cover.The coveris removed, cables are placedin the channel, and then the coveris replaced.Open cablemanagement can lookmessierif notmaintained well, but closed cablemanagement oftenis used to hide huge loops of cables that are too long.When closed cablemanagement fills up,it becomes difficult orimpossible to replace the covers, so they are left off, andit becomes even messier than open cablemanagement.Closed cablemanagementis alsomore tedious to work with and becomes a nuisance for very little gain.
Some racks are designed to have vertical cablemanagement as a recessed channel between the racks.Others can haveit within the rack, going down the sidesjustinside the back posts.Others can have cablemanagement attached only externally to the back posts.Cablemanagement thatis between the racks makes cables take up more valuable floor space. Cable management that attaches to the back of the racks protrudesinto the aisles, whichmakes the cablesmore vulnerable andmay be a safety concern.Cablemanagement that goes within the rack requires racks that are deep enough to contain the cable management, in addition to the deepest piece of equipment.Wherever it is placed, the cablemanagement can be either open or closed.
Cablemanagement also comesin a variety of widths.A data center typ- ically requires different widths for different rack functions.Racks that have lots of patch panels and network or console equipment will have lots of ca- bles in them and require much wider and deeper cable management than racks that contain a few hosts with a few network and console connections. Racks with lots of wires also require lots of horizontal cable management well distributed between the pieces of equipment and the various patch pan- els.Having too little cable-management space is frustrating and encourages adhoc solutions that are difficult tomanage.Thatmakesit difficult to access the cables, and SAsmay damage cables by trying to force them into the cable management.It is better to overestimate rather than to underestimate your space requirements.
6.1.6.8 Strength
The racksmust be strong enough to carry the weight of the equipment that will bemountedin them.As stated before, earthquake zonesmay have special strength requirements.
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6.1.6.9 Environment
If your racks are going to be deployed in remote locations, consider the atmosphere of the location.For example,in China, the pervasive use of coal resultsin air pollution thatis high in sulfur.The sulfur leads to high water vapor content in the air, which leads to racks rusting.Special coatings are available that prevent rusting.
6.1.6.10 Shelves
Smaller equipment not designed tomountin a rack can sit on a shelf.Shelves thatmountinto racks are available.
Be careful how shelves and various pieces of rack-mount equipment will fitinto the rack and how, or whether, you can combine different rack-mount units in the same rack or whether you can still mount shelves in the rack when a rack-mount unit requires the vertical rails to be moved forward or backward.Often, large rack-mount units need the vertical rails to be a par- ticular distance apart so they can be attached at all four corners. In some cases, the positioning of these rails may prevent you from mounting other pieces of equipment that require a different spacing of the rails.Worse yet, the shelvesmay require these vertical rails to have an exact positioning thatis not compatible with your rack-mount equipment.Make sure that the racks you choose allowmounting the shelves with the vertical railsin various po- sitions.You alsomay want to get extra vertical rails so that you canmount a couple of units with different depthsin the same rack.
6.1.6.11 Extra Floor Space
Consider howmany large freestanding pieces of equipment youmight have, with a footprint the size of a rack or larger, that cannot be rack-mounted. Leaving space for theseitems will affect the number of racks that you order and how you wire the data center.
6.1.7 Wiring
Itis difficult to keep data center wiring tidy.However, when you are designing the data center, you have several ways tomakeit easier for all the SAs to keep the wiring neat.
Hiding themess does notmean thatitis not there or thatit will not affect SAs trying to workin the data center.A raised floor can hide sloppy cabling, with cables following all sorts of randompaths to go between two points. When you go to pull cables out from under the floor, you will find them