Cost-effective data transfer for data creation and data recovery - Reliability Assurance of Big Data in the Cloud - page 77

7.5.3 Task completion time comparison
In addition to the energy consumption comparison just mentioned, we also com-
pared the task completion time by applying the three data transfer strategies. Based
on simulations conducted with different maximumBW and deadline values, Fig-
ure 7.10 shows the average completion time of transferring data files by using the
three data transfer strategies. The horizontal axis is the data size and the vertical
axis is the proportion of time from startTime to the end of the data transfer task in
the maximum data transfer duration. From this comparison we find that the energy
saving of the LRCDT strategy is achieved without sacrificing too much data transfer
time. Although it can be seen in Figure 7.10 that the task completion time using
LRCDT is more than the maximum-speed strategy, the task completion time is still
much shorter than the maximum data transfer duration. In general, compared to the
maximum-speed strategy that transfers data files with the shortest time, the average
transfer time increment of LRCDT is 37.9%. Apart from the fast increment for trans-
ferring data files between 1 MB and 1 GB, for transferring the data files from 1 to 10
GB the average transfer time increment of LRCDT drops by 27.8%. Meanwhile, the
average transfer time of LRCDT is 27.5% shorter in comparison to the minimum-
speed strategy. This means that LRCDT can finish the data transfer task with 27.5%
less time. The reason for the fast increment in task completion time when data size is
between 1 MB and 1 GB is that, when the data size is small, minimumBW is smaller
than the current available bandwidth of most of the routers. Hence, LRCDT is able to
allocate bandwidth without increasing the link rates of routers. The available band-
width of each timeslot is allocated quickly so that the task completion time incurs
a rapid increase. When the data size reaches about 1 GB, the link rates of routers
are increased so that more bandwidth can be allocated and the task completion time
drops quickly.
Figure 7.10 Comparison of average completion time