Note: This blog is written with help of my friend Rajanikanth Katikitala
Green IT
• Use servers with less power demands. The lower the PUE, the more efficient data center infrastructure
Power Usage Efficiency = Total facility Power
-------------------------------
Total IT equipment Power
• Floor space reduction by moving to high density blade servers
• Use hot & cold aisle containments to avoid mixing of hot air with cold air
• Use rack or row cooling instead of traditional CRAC units
• Use free cooling. Retrofit outside air supply where possible
• Right size the cooling requirement as per the IT load to avoid over sizing cooling.
• use high density area to focus on cooling
• Distribute high-density racks throughout the layout to mitigate hot
• spots; use spot rack cooling as necessary
The Uptime Institute “tiers”
The uptime Institute classifies data
centers according into “tiers”. The following table is taken from
the paper, “Industry Tier Classifications Define Site Infrastructure
Performance,” by W. Pitt Turner IV and Kenneth Brill, both of the UpTime
Institute.
Tier I
|
Tier II
|
Tier III
|
Tier IV
|
|
Number of delivery paths (of power
and a/c etc)
|
Only 1
|
Only 1
|
1 active
1 passive
|
2 active
|
Redundant components
|
N
|
N+1
|
N+1
|
2(N+1) or S+S
|
Support space to raised floor
ratio
|
20%
|
30%
|
80-90%
|
100%
|
Initial watts/sq ft
|
20-30
|
40-50
|
40-60
|
50-80
|
Ultimate watts/sq ft
|
20-30
|
40-50
|
40-60
|
150+
|
Raised floor height
|
12”
|
18”
|
30-36”
|
30-36”
|
Floor loading pounds/sq ft
|
85
|
100
|
150
|
150+
|
Utility voltage
|
208, 480
|
208, 480
|
12-15Kv
|
12-15Kv
|
Months to implement
|
3
|
3-6
|
15-20
|
15-20
|
Year first deployed
|
1965
|
1970
|
1985
|
1995
|
Construction $/sq ft raised floor
|
$450
|
$600
|
$900
|
$1,100
|
Annual IT downtime due to site
|
28.8 hrs
|
22.0 hrs
|
1.6 hrs
|
0.4 hrs
|
Site availability
|
99.671%
|
99.749%
|
99.982%
|
99.995%
|
“Even a fault-tolerant and concurrently maintainable Tier IV
site will not satisfy an IT requirement of “Five Nines” (99.999%) uptime. The
best a Tier IV site can deliver over time is 99.995%, and this assumes a site
outage occurs only as a result of a fire alarm or EPO (Emergency Power Off),
and that such an event occurs no more than once every five years. Only the top
10 percent of Tier IV sites will achieve this level of
performance. Unless human activity issues are continually and
rigorously addressed, at least one additional failure is likely over five
years. While the site outage is assumed to be instantaneously
restored (which requires 24 x “forever” staffing), it can still require up to
four hours for IT to recover information availability.
Tier IV’s 99.995% uptime is an average over five
years. An alternative calculation using the same underlying data is
100% uptime for four years and 99.954% for the year in which the downtime event
occurs. Higher levels of site uptime can be achieved by protecting
against accidental activation or the real need for fire protection and
EPOs. Preventatives include high sensitivity smoke detection, limiting
fire load, signage, extensive training, staff certification, limiting the
number of “outsiders” in critical spaces, and treating people well to increase
pride in their work. All of these measures, if taken, can reduce the risk of
failures. Other solutions include placing the redundant parts of the
IT computing infrastructure in different site infrastructure compartments so
that a site infrastructure event cannot simultaneously affect all IT
systems. Another alternative is focusing special effort on
business-critical and mission-critical applications so they do not require four
hours to restore. These operational issues can improve the availability
offered by any data center, and are particularly important in a “Four Nines”
Tier IV data center housing IT equipment requiring “Five Nines” availability.”
Heating Ventilation
and Air Conditioning standards
The Uptime Institution recommends hot and cold
aisles. Instead of having the fronts of all racks facing one way,
racks in raised floor data centers should be installed with the fronts towards
each other (the cold aisle) and the backs towards each other (the hot
aisle).
ASHRAE "TG9 HDEC" is the industry guiding reference
document for data center environments in the US. According to it the data
center ambient temperature should be from 20o C (68o F)
to 25o C (77o F) and measured in the cold aisle
at 5 ft. above the raised floor at the air intake of the operating equipment. The
relative humidity should be from 40 to 55%. The future TIA-942
standard will be comparable to the ASHARE standard. The TIA-942 standard will
call for a maximum rate of change of 5o C (9o F)
per hour.
“Operationally, an
errpr on the slightly cooler (21-22 deg C 70-72deg F) room ambient measured at
an average 3-5' off the floor in the center of the
aisles. Experience has shown that prolonged temperatures in the room
above 75-78 deg. F (24-26C) reduce HDD life up to 50% and cause serious
internal issues as interior processor temperatures can exceed 40 deg. C (105
deg. F)”.
If you are involved in writing a proposal that calls for data
center temperatures, it is strongly recommended that SLAs state that the HVAC
system will keep equipment within the temperature ranges specified by OEM
equipment manufacturers, rather than the air temperatures mentioned
above. If a loss of city water supply causes a cooling emergency,
you will bless that bit of advice.
Rack spacing
Based on studies that Jonathon Jew performed at 12 web hosting
data centers between 30% to 60% of the computer room space can be consumed by
power & cooling equipment and circulation (compare with the UpTime table’s
entries for Support space to raised floor ratio). He comments that:
“… a lot depended on the heat density of the computer room, the shape of the
computer room, and the quantity and size of columns.”
That reference to circulation concerns rack spacing and other
passageways. The ASHRAE and ANSI/TIA recommendations for cabinet/rack spacing
are to provide a minimum of 4 feet clearance in the cold aisles in front of
cabinets and 3 feet clearance in the hot aisles behind cabinets. The
Americans with Disabilities Act dictates a minimum of 3 feet for any aisles
where wheel chairs need to traverse. Jonathon says: “For
cabinets/racks with equipment with a depth no greater than 2 feet, you may be
able to get by with rows of cabinets/racks spaced on 5 feet centers. However,
the recommended spacing based on ASHRAE and ANSI/TIA is 7 ft centers.”
If your customer has HP 42
U racks (24” wide and close to 40” deep) with 4 foot of clearance for the cold
aisle and the 3 foot of clearance in the hot aisle there will be two racks
occupying 164” x 24”. That’s 13.7 square feet per rack including the
hot and cold aisles but ignoring any other additional passageways
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