rack spacing?

Unanswered Question
Mar 9th, 2009

I would like to solicit other's opinions on racking Cisco 2960 switches & 2811 routers. What kind of dead space is needed/required/optimal between devices mounted in a rack? Are fans required to circulate air, or are the little fans in each device sufficient for cooling?

Thanks for any candor shared.

I have this problem too.
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scottmac Mon, 03/09/2009 - 19:17

Spacing is nice if you have the real estate / rail space.

If not, you can pack the rails ... but cooling and ventilation is critical ... make sure you have some backup system for your cooling and ventilation.

Giving the equipment a little breathing room is a good thing, Fans are required to circulate the air ... the denser the rack, the more critical it is, as is hot/cold zone management.

If the rack is spread out a little, and the room temperature is cool, extra fans are not generally necessary.

If the equipment is in a cabinet, fully enclosed, then you need circulation within the cabinet and fans to circulate cooler air into the cabinet. Moving warm / hot air around inside does no good.

Good Luck

Scott

ericn8484_2 Tue, 03/10/2009 - 05:11

There are a number of factors that play into your cooling.

First, is it an open rack or a closed rack?

Second, are there other devices in this rack such as servers?

Third, what type of cooling and size is the room that these pieces of equipment will be in.

The only place where we have Cisco equipment that has any sort of fan are enclosed half racks that sit in the ceiling of our floors. Only then do we have around a 5 inch fan to move air in and out of the cabinet. These devices don't usually produce much heat and as long as there is a place for the air to go, you wont need to worry about additional cooling.

Also, you DO NOT want to put spacing between equipment in racks, while it seems like a good way to allow air between the units, unless it is a completely open racking, you are creating hot pockets for air that can't move around and that will make it worse for your equipment. That is why the equipment has fans in the back to blow the hot air out the back and out of the rack.

ocicat002 Tue, 03/10/2009 - 13:29

Thank both of you for your responses. I have a few follow-up questions:

* Is the ventilation/circulation in enclosed racks predictably bad? In what little price comparisons I have made, enclosed cabinets are (obviously) more expensive, but I haven't seen much on the effectiveness of the ventilation.

* I'm willing to go with an open rack, & if I do, should I be able to provide no space between Cisco devices?

I do intend to mix in some 1U & 4U servers along with some Sun Ultra 5's on shelves.

Your continued candor is greatly appreciated.

scottmac Tue, 03/10/2009 - 14:22

Enclosed cabinets require a good fan at the top or bottom, or both. SO far my favorite fan is the "pagoda" fan - sort of like a sideways squirrel cage fan; it moves a lot of air, and is relatively quiet (not that it matters in a room full of loud fans).

A popular option is to use a 23" telco rack with 19" spacers or rail settings. The extra space on the sides provides a good ventilation channel, and room for the cabling races without choking the equipment.

It helps to pair up the equipment with the cabinets; some ventilate sideways, some ventilate front-to-back ... if you use a lot of front-to-back equipment, then a door that can breath might be a good thing. If the equipment ventilates side-to-side, then you want to make sure that a good air channel is maintained and that the air can flow freely in that direction.

Good Luck

Scott

ericn8484_2 Wed, 03/11/2009 - 04:49

Enclosed cases give you another level of physical security if its a location that others can get to. The trade off is that they can build up heat which is why they are typically well vented and faned systems assocated with them.

As scott mentioned, the popular racks are the 23" telco racks with 19" spacers.

If you are going to have servers and network gear in the same rack, start installing them in the middle of the rack and as you install new equipment go up and down at the same time so you are filling outwards.

Heat always moves up so you never want pockets in your equipment because its a heat build-up area. Servers will typically always go to the back of the rack so place them on the bottom where a lot of switches and such only goes about halfway to the back of the rack so place them at the top.

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