\documentclass[tikz]{standalone}
\usetikzlibrary{positioning,shapes.geometric,shapes.symbols,shadows,fit}
\begin{document}
\begin{tikzpicture}[%
		node distance=1em,
		task/.style={regular polygon,regular polygon sides=3,text width=2.5em,draw},
		share/.style={cylinder,shape border rotate=90,aspect=.3,text width=2.5em,text height=1em,draw},
		client/.style={cloud,aspect=2}
		]
	\node (C1) [client,inner sep=0pt,draw] {Client\textsubscript{1}};
	\node (C2) [client,inner sep=0pt,draw,right=of C1] {Client\textsubscript{2}};
	\node (CD) [right=of C2] {\ldots};
	\node (CN) [client,inner sep=0pt,draw,right=of CD] {Client\textsubscript{n}};

	% line between server and browser
	\draw [dotted] ([xshift=-7em,yshift=-.8em]C1.south west) node[left,above]{browser} node[left,below]{server(s)} -- ([xshift=5em,yshift=-.8em]CN.south east);

	\node[task,inner sep=-4.5pt,below=of C1,fill=white,xshift=6.5em,yshift=-4.5em] (Tn) {Task\textsubscript{n}};
	\node[task,inner sep=-4.5pt,below=of C1,fill=white,xshift=5em,yshift=-3.0em] (Td) {\ldots};
	\node[task,inner sep=-4.5pt,below=of C1,fill=white,xshift=3.5em,yshift=-1.5em] (T2) {Task\textsubscript{2}};
	\node[task,inner sep=-4.5pt,below=of C1,fill=white,xshift=2em] (T1) {Task\textsubscript{1}};

	\node[share,node distance=6em,right=of T1,fill=white,xshift=4.5em,yshift=-4.5em] (Sn) {SDS\textsubscript{n}};
	\node[share,node distance=6em,right=of T1,fill=white,xshift=3em,yshift=-3.0em] (Sd) {\ldots};
	\node[share,node distance=6em,right=of T1,fill=white,xshift=1.5em,yshift=-1.5em] (S2) {SDS\textsubscript{2}};
	\node[share,node distance=6em,right=of T1,fill=white] (S1) {SDS\textsubscript{1}};

	\node[fit={(T1)(Sn)},draw] (TS) {};

	% line between client and server
	\draw [dotted] ([xshift=-7em,yshift=-11em]C1.south west) node[left,above]{server(s)} node[left,below]{device(s)} -- ([xshift=5em,yshift=-11em]CN.south east);

	% device 1
	\node[task,text width=1.5em,inner sep=-4.5pt,node distance=12em,below=of C1,double copy shadow={shadow xshift=.4em,shadow yshift=-.4em},fill=white] (D1T1) {};
	\node[share,text width=.3em,text height=.8ex,right=of D1T1,double copy shadow={shadow xshift=.4em,shadow yshift=-.4em},fill=white] (D1S1) {};

	\node[draw,fit={(D1S1)(D1T1)([shift={(1.2em,-1.2em)}]D1S1.south east)},label=below:{\scriptsize mTask device\textsubscript{1}}] (D1) {};

	% device 2
	\node[task,text width=1.5em,inner sep=-4.5pt,node distance=12em,below=of C2,double copy shadow={shadow xshift=.4em,shadow yshift=-.4em},fill=white] (D2T1) {};
	\node[share,text width=.3em,text height=.8ex,right=of D2T1,double copy shadow={shadow xshift=.4em,shadow yshift=-.4em},fill=white] (D2S1) {};

	\node[draw,fit={(D2S1)(D2T1)([shift={(1.2em,-1.2em)}]D2S1.south east)},label=below:{\scriptsize mTask device\textsubscript{2}}] (D2) {};

	% device ...
	\node[right=of D2] {\ldots};

	% device n
	\node[task,text width=1.5em,inner sep=-4.5pt,node distance=12em,below=of CN,double copy shadow={shadow xshift=.4em,shadow yshift=-.4em},fill=white] (DNT1) {};
	\node[share,text width=.3em,text height=.8ex,right=of DNT1,double copy shadow={shadow xshift=.4em,shadow yshift=-.4em},fill=white] (DNS1) {};

	\node[draw,fit={(DNS1)(DNT1)([shift={(1.2em,-1.2em)}]DNS1.south east)},label=below:{\scriptsize mTask device\textsubscript{n}}] (DN) {};

	% iTask server
	\node[fit={(C1)([shift={(1em,-1.2em)}]DN.south east)},draw,label={iTask server}] {};

	% Arrows
	\draw [<->] (C1) -- (T1);
	\draw [<->] (C2) -- (T1);
	\draw [<->] (CN) -- (T1);

	\draw [<->] (T1) -- (S1);
%	\draw [<->] (T1) -- (S2);
%	\draw [<->] (T1) -- (Sn);

	\draw [<->] (Tn) -- node [midway,above,fill=white] {\small\texttt{liftmTask}} (D2T1);
	\draw [<->] (Sn) -- node [midway,above,fill=white] {\small\texttt{liftsds}} (D2S1);

	\draw [<->] (D1T1) -- (D1S1);
	\draw [<->] (D2T1) -- (D2S1);
	\draw [<->] (DNT1) -- (DNS1);

	\draw [<->] (D1.north) to [in=180,out=135] node [midway,above,fill=white] {\small\texttt{withDevice}} (TS.west);
\end{tikzpicture}
\end{document}
