From a615b61e97511ba656d6ef154141083fa2ce9a61 Mon Sep 17 00:00:00 2001
From: mjkwiatkowski <mati.rewa@gmail.com>
Date: Wed, 15 Jul 2026 13:35:47 +0200
Subject: feat: fixed the comments from Dante about section 2.2

---
 content/background.tex | 64 +++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 48 insertions(+), 16 deletions(-)

(limited to 'content/background.tex')

diff --git a/content/background.tex b/content/background.tex
index 5ab53dc..8349bcf 100644
--- a/content/background.tex
+++ b/content/background.tex
@@ -4,33 +4,66 @@
 	The contribution in this chapter is three-fold:
 
 	\begin{enumerate}[label=\emph{C\textsubscript{\arabic*}}, itemsep=0.2pt]
-		\item We provide a brief overview on datacenter simulation (\Cref{sss:simulation}), compute failures (\Cref{sss:failures}), and digital twinning (\Cref{sss:what_is_digital_twinning}).
-		\item We survey the state-of-the-art concerning datacenter digital twinning (\Cref{ss:digital_twins_for_datacenters}).
+		\item We provide a brief overview on datacenters (\Cref{ss:datacenters}) datacenter simulation (\Cref{sss:simulation}), compute failures (\Cref{sss:failures}), and digital twinning (\Cref{ss:digital-twinning}).
+		\item We survey the state-of-the-art concerning datacenter digital twinning (\Cref{sss:advanced_dts}).
 		\item We construct a system model for existing datacenter digital twins (\Cref{ss:system_model_for_dcdts})
 	\end{enumerate}
 \end{mynote}
 
 \section{Datacenters}\label{ss:datacenters}
-In this section we provide a short background on datacenter simulation and compute failures.
-We find it useful to provide a brief introduction to both topics so as to ensure reader's fullest understanding of subsequent chapters.
-Since datacenters are important building blocks of the digital society, reliable warehouse management is a key priority for datacenter operators.
-Incorrect management decisions can lead to missed \gls{sla}s~\cite{DBLP:journals/corr/IosupKLVG22} and even large financial penalties~\cite{DBLP:report/AnnualOutageAnalysis2025}.
-However, efficient and timely management is a difficult challenge, because datacenters are extremely complex facilities.
-To help datacenter operators, the scientific community proposes to simulate datacenters to make more informed decisions.
+In this section we provide a short background on datacenters, datacenter simulation and compute failures.
+We find it useful to provide a brief introduction to these topics so as to ensure reader's fullest understanding of subsequent chapters.
+%What are the parts of a data center? 
+
+A datacenter is ``a physical room, building, or facility for the purpose of the storage, management, and dissemination of data and information, including training artificial intelligence, housing IT infrastructure, computer systems, and associated components.''~\cite{Wikipedia:article/Datacenter}.
+In essence, datacenters contain a large amount servers, and everything that is needed to maintain them.
+Most often servers are specially-designed motherboards with a (multicore) \gls{cpu}, \gls{ram} and storage.
+More diverse servers include a \gls{cpu}, \gls{tpu}, or \gls{npu}.
+To efficiently organize the datacenter, servers are placed within server \emph{racks}.
+To maintain a large number of server racks, datacenters contain a cooling system to control the heat transfer and temperature of both the hardware and the entire facility.
+Additionally, datacenters consume vast amounts of electricity~\cite{Wikipedia:article/Datacenter}.
+Because of this, the datacenter power supply play a critical role in keeping the services running on the servers always available.
+An example datacenter in \gls{cern}, is depicted on \Cref{fig:datacenter}.
+
+\begin{figure}[t]
+	\centering
+	\includegraphics[width=0.9\linewidth]{images/datacenter.jpg}
+	\caption[Datacenter in CERN.]{Example of a datacenter in \gls{cern}, Switzerland (2010)~\cite{Wikipedia:article/Datacenter}. In the figure we can see servers within servers racks, and the network cables.}
+	\label{fig:datacenter}
+\end{figure}
+
+%Who are the stakeholders? 
+Datacenters form the backbone of the digital society.
+The main stakeholders, besides the companies in the \gls{it} sector, are intelligent healthcare, remote work, online gaming, digital government and education, banking and finance, transport and logistics~\cite{DBLP:journals/corr/IosupKLVG22}.
+All of the above industries need reliable datacenters to work well in the 21\textsuperscript{st} century.
+
+%Where does the actual complexity come from?
+The high demand for online services drives datacenter complexity.
+Moreover, due to the Jevon's paradox of Computer Systems~\cite{Wikipedia:article/JevonsParadox}, improved availability increases the demand.
+As a result, datacenters contain hundreds, or even thousands of hardware components.
+Every device may have a different vendor, new configuration, unusual interface \etc
+Because of this, datacenter operators are often faced with difficult operational and architectural challenges~\cite{Wiley:book/Condor2005,DBLP:conf/ccgrid/MastenbroekAJLB21}, which span software and performance engineering.
+Making sure that all the parts of the datacenter work together is a tough task.
+What drives datacenter complexity even further is that sophisticated systems are not merely a sum of their parts~\cite{Wikipedia:article/Systems_Thinking}.
+The combination of the above factors makes datacenter management a difficult, non-trivial challenge.
 
 \subsection{Datacenter Simulation}\label{sss:simulation}
 \input{sources/simulator_comparison.tex}
+
+Efficient and timely datacenter management is a difficult challenge, because datacenters are extremely complex facilities.
+They require deep understanding to operate properly.
+However, running real-world experiments is costly in both time and resources.
+Additionally, experimentation \emph{in situ} is unsustainable and difficult to reproduce.
+Alternatives to real-world experiments include simulation and mathematical analysis.
+Because mathematical analysis is not scalable to modern datacenters~\cite{DBLP:conf/ccgrid/MastenbroekAJLB21}, in this project we only consider simulation as a foundation for the \gls{dcdt}.
+%To help datacenter operators, the scientific community proposes to simulate datacenters to make more informed decisions.
+
 Simulation empowers better design, testing and management of datacenters~\cite{DBLP:conf/ccgrid/MastenbroekAJLB21}.
 A well-designed datacenter simulator can estimate a months-long workload in a few minutes or hours.
 To simulate is to ``imitate of real-world process or system over time, enabling the study of, and experimentation with the internal interactions of complex systems''~\cite{DBLP:books/daglib/0034857}
 In this project we only consider  \emph{discrete-event simulation}.
-
 Discrete-event simulation represents system operations as a sequence of events over time, with an assumption that no changes occur between the events.
 Due to the scale and complexity of datacenters, most simulators use discrete-event simulation~\cite{DBLP:conf/ccgrid/MastenbroekAJLB21}.
-
-Alternatives to simulation include real-world experimentation and mathematical analysis.
-However, experimentation \emph{in situ} is unsustainable, expensive and difficult to reproduce and mathematical analysis is not scalable to modern datacenters~\cite{DBLP:conf/ccgrid/MastenbroekAJLB21}.
-Therefore, in this project we only consider simulation as a foundation for the \gls{dcdt}.
 There exist many datacenter simulation tools, for example DGSim~\cite{DBLP:conf/europar/IosupSE08}, CloudSim~\cite{DBLP:journals/spe/CalheirosRBRB11}, SimGrid~\cite{DBLP:journals/corr/CasanovaGLQS13}, iCanCloud~\cite{DBLP:journals/grid/NunezVCCCL12}, GroudSim~\cite{DBLP:conf/europar/OstermannPPF10} and OpenDC~\cite{DBLP:conf/ccgrid/MastenbroekAJLB21}.
 See \Cref{tab:datacenter_simulator_comparison} for a comparison of selected datacenter simulators, combined by Mastenbroek \etal~\cite{DBLP:conf/ccgrid/MastenbroekAJLB21}.
 In order to narrow the scope of the project, we only consider {OpenDC} as a simulator for the digital twin design.
@@ -54,11 +87,10 @@ A failure model consists of two statistical distributions:
 	\item to model service unavailability
 	\item to model service availability.
 \end{enumerate*}
-A failure trace is defined by an interval, duration, and intensity of several failures, which are later looped throughout the simulated workload (source \url{opendc.org}).
+A failure trace is defined by an interval, duration, and intensity of several failures, which are later looped throughout the simulated workload~\cite{GitHub:software/OpenDC}.
 In summary OpenDC enables experimentation with failures that enables insights that are not provided by other state-of-the-art software.
 However, the fidelity of failure modeling inside a datacenter simulation is still insufficient to predict in failures in real-time, as they happen in a physical datacenter.
 Since a datacenter simulator is quite different from a digital twin, we cannot use the same computation methods from simulation to predict real-time failures.
-Digital twinning is an improvement upon pure simulation.
 \begin{figure}[t]
 	\centering
 	\includegraphics[width=0.95\linewidth]{images/five_dimensional_dt.pdf}
@@ -225,7 +257,7 @@ Kalibre takes the best of both \gls{ml} and \gls{cfd} approaches and achieves su
 
 \begin{figure}[t]
 	\centering
-	\includegraphics[width=0.95\linewidth]{images/system_model.pdf}
+	\includegraphics[width=0.95\linewidth]{images/system_model.png}
 	\caption[A system model for datacenter digital twins.]{A generic system model for datacenter digital twin deployments.
 		The design of DyTwin~\cite{DBLP:conf/sc/TaheriBPRHDEWPM24}  indirectly incorporates in its architecture a ``virtual-to-virtual`` digital thread between different digital twins.
 		Zhao \etal likewise present key elements to the digital thread in their architecture~\cite{DBLP:conf/AppliedEnergy/Zhao20}. We add the \emph{Digital Thread} to our model explicitly.}
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