Information Technology Reference
In-Depth Information
4.3
Performance Index, Total Cost of Ownership, and Cost-Performance Ratio
Eq. (1) calculates the average access time (AAT) for each data size. In Eq. (1),
ijk
AAT
represents average access time with the same data size, and
i
N
represents the
current data size. The following three formulae will evaluate the performance
index
(PI) [1][2]. Eq. (2) calculates the data center's average access times overall
AAT
s
jk
for each test (i.e. write, read, remote backup), in which
AAT
represents the average
access time of each data size, please refer back to Eq. (1). Eq. (3) calculates the data
center's normalized performance index. Eq. (4) calculates the data center's
performance index overall,
s
ijk
SF
is constant value and the aim is to quantify the value
1
for observation.
AAT
ijk
(1)
AAT
=
,
where
i
=
1
2
,...,
l
,
j
=
1
2
,...,
m
,
k
=
1
2
,...,
n
s
ijk
N
ik
l
l
∑
∑
(2)
AAT
=
ˉ
⇅
AAT
,
where
j
=
1
2
,...,
m
,
k
=
1
2
,...,
n
,
ˉ
=
1
s
i
s
i
jk
ijk
i
=
1
i
=
1
1
AAT
s
jk
(3)
PI
=
,
where
j
=
1
2
,...,
m
,
k
=
1
2
,...,
n
jk
⊛
⊞
1
⊜
⊝
⊟
⊠
MAX
⊜
⊟
AAT
h
=
1
2
,...,
m
s
hk
⊛
n
⊞
n
∑
∑
⊜
⊟
2
(4)
PI
=
W
⇅
PI
⇅
SF
,
where
j
=
1
2
,...,
m
,
k
=
1
2
,...,
n
,
SF
=
10
,
W
=
1
⊜
⊜
⊟
⊟
j
k
jk
1
1
k
⊝
⊠
k
=
1
k
=
1
The total cost of ownership (TCO) [1][2] is divided into four parts: hardware costs,
software costs, downtime costs, and operating expenses. The costs of a five-year
period
Cost
are calculated using Eq. (5) where the subscript
j
represents various
data center and
g
stands for a certain period of time. Among it, we assume there is
an annual unexpected downtime,
jg
, the monthly expenses
Cost
downtime
for
server
a
, including machine room fees, installation and setup fee,
provisional changing fees, and bandwidth costs.
Cost
⇅
period
monthly
b
∑
∑
∑
∑
Cost
=
Cost
+
Cost
⇅
period
+
Cost
+
Cost
,
jg
downtime
for
server
monthly
hardware
software
a
b
c
d
(5)
a
b
c
d
where
j
=
1
2
,...,
m
,
g
=
1
2
,...,
o
This section defines the cost-performance ratio (C-P ratio) [10],
, of each data
CP
jg
center based on total cost of ownership,
, and performance index,
PI
, as shown
CP
jg
j
in Eq. (6). Eq. (6) is the formula for C-P ratio where
SF
is the constant value of
scale factor, and the aim is to quantify the C-P ratio within the interval of (0,100] to
observe the differences of each data center.
2
PI
j
CP
=
⇅
SF
,
jg
2
Cost
(6)
jg
4
where
j
=
1
,...,
m
,
g
=
1
,...,
o
,
SF
=
10
2
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