content for airco, security in datacenters

Filled some content for review

datacenters/datacenters_201.rst

@@ -22,8 +22,88 @@ Cooling
 N+1, N+2 
 ---------
 
+The cooling exhausts for redundant or load-sharing aircos should be 
+located in enough distance from each other that they do not influence each
+others effectiveness.
+
+Cooling efficiency
+------------------
+
+Surrounding temperature and load both influence how good an airco can work.
+For example it will work best if it's not fully loaded (has to move as many 
+units of thermal heat as it's specified for) and if the outside temp is 
+somewhere below 30Deg Celsius. 
+(Hopefully someone knows a smart formula for that)
+Their effectiness drops if they're located too close to places where hot air
+is not really moving, i.e. ground level or non-raised on a rooftop, or on a
+roof section that is surrounded by higher parts of the building.
+Spraying water with a sprinkler can help.
+
+Cooling failures
+----------------
+
+Very important is to gather information on the duration of a cooling failure
+so far. The surrounding datacenter structures delay a failures effect by
+absorbing heat. 
+That means two things:
+1. At some point the walls have gained a temperature close to the ambient.
+From that moment, they will not absorb more heat, resulting in a massive
+increase of the rate at which the room is heating up
+2. A sliding delay that means the room will take somewhat as long as it took
+to heat up to cool down again, even if you already shut down everything that
+consumes power.
+
+Generally you need to assess a few things:
+- is the temperature currently still a tolerable operating temperature
+- how quicky is it rising
+- how soon will the fault be fixed and when will a tolerable temperature be
+reached
+- how long is the expected time of overheating
+
+- what damage to expect from quick heatup and cooldown
+(i.e. tape backups in progress at the time of failure will be probably lost 
+because of the stretching effects on the media. Disks can fail by the dozen at
+the same time)
+
+- what are the absolutely critical systems running, and how much power do the use
+- how many not absolutely critical systems are running, and how much power will
+it save to turn them off. 
+- How fast can you shut them down? (i.e. on Unix, that could mean init 2, wait,
+ flip the switch)
+- can you shut down enough to keep the most critical systems running?
+- can you also shut down enough to massively flatten the temperature curve?
+
+Generally, the goal is to flatten the effects so that the critical 
+infrastructure gets away with a very and constant slow hike up and down at 
+less than 2-3 deg / hr.
+This is also to be respected when the cooling is fixed again, it should run
+at emergency power only till the pivot is taking off the curve and the the
+power needs to be constantly decreased so the ambient takes a slow fall instead
+of going from 55C to 21C in 30 minutes.
+(Dangers: Humidity, microscopic tears on PCB)
+
+
 Physical security and common security standards compliance requirements
 =======================================================================
 
 Suggested practices
 ===================
+
+Access control
+--------------
+
+Security should require a ID from anyone coming onsite, and not stop
+at having you fill a form where you just write anything you want.
+
+Techs should need to bring a ticket ID, and this ticket ID plus the tech's
+name should be announced by the vendor to security, plus(!) a callback to
+a defined number known to security. So, a double handshake with a token.
+This is really important to avoid incidents like suddenly missing two 
+servers because "there were some techs that replaced it"
+
+Most critical DCs will have security accompanying you to the server.
+Some will keep the sec person around while the tech is working.
+The really smart ones train their sec stuff so that they will know *which* 
+server the tech needs to go to and *which* disk is to be replaced as to the
+original ticket. (If you think the security people can't handle that, then
+just ask yourself who's to blame since it does work for other DCs)

datacenters/datacenters_301.rst

@@ -10,6 +10,20 @@ PUE (Power Usage Effectiveness)
 3 phase power
 -------------
 
+Note you can't use a wire clamp to measure a 3-phase power cable, you need to 
+measure each phase by itself.
+
+DC power
+--------
+
+48V (telco land, NEBS standard) and other versions that are being tried, 
+(12, 24V).
+Grounding requirements, power bars. Devices often have different plugs.
+Most of the time still using A+B circuits
+Reduced conversions == Reduced losses. Amplified by most larger servers (i.e. 
+HP C7000, SuperDome) using 48V internally.
+Even more interesting with large UPS banks since those also use 48V.
+
 Increasing cooling efficiency
 =============================