At 7:06 PM +0000 3/29/08, Paul Vixie wrote:
While the chilled water door will provide higher equipment density per rack, it relies on water piping back to a "Cooling Distribution Unit" (CDU) which is in the corner sitting by your CRAC/CRAH units.
it just has to sit near the chilled water that moves the heat to the roof. that usually means CRAC-adjacency but other arrangements are possible.
When one of the many CRAC units decides to fail in an air-cooled environment, another one starts up and everything is fine. The nominal worse case leaves the failed CRAC unit as a potential air pressure leakage source for the raised-floor and/or ductwork, but that's about it. Chilled water to the rack implies multiple CDU's with a colorful hose and valve system within the computer room (effectively a miniature version of the facility chilled water loop). Trying to eliminate potential failure modes in that setup will be quite the adventure, which depending on your availability target may be a non-issue or a great reason to consider moving to new space. /John