▁can ▁often ▁be ▁placed ▁strateg ically ▁close ▁to ▁or ▁within ▁sites ▁where ▁users ▁need ▁them . ▁However , ▁rep lication ▁of ▁datasets ▁and ▁creation ▁of ▁rep lic as ▁is ▁bound ▁by ▁the ▁avail ability ▁of ▁storage ▁within ▁sites ▁and ▁band width ▁between ▁sites . ▁The ▁rep lication ▁and ▁creation ▁of ▁rep lica ▁datasets ▁is ▁controlled ▁by ▁a ▁rep lica ▁management ▁system . ▁The ▁rep lica ▁management ▁system ▁determ ines ▁user ▁needs ▁for ▁rep lic as ▁based ▁on ▁input ▁requests ▁and ▁creates ▁them ▁based ▁on ▁avail ability ▁of ▁storage ▁and ▁band width . ▁All ▁rep lic as ▁are ▁then ▁catalog ed ▁or ▁added ▁to ▁a ▁directory ▁based ▁on ▁the ▁data ▁grid ▁as ▁to ▁their ▁location ▁for ▁query ▁by ▁users . ▁In ▁order ▁to ▁perform ▁the ▁tasks ▁undert aken ▁by ▁the ▁rep lica ▁management ▁system , ▁it ▁needs ▁to ▁be ▁able ▁to ▁manage ▁the ▁underlying ▁storage ▁infrastr ucture . ▁The ▁data ▁management ▁system ▁will ▁also ▁ensure ▁the ▁tim ely ▁updates ▁of ▁changes ▁to ▁rep lic as ▁are ▁propag ated ▁to ▁all ▁nodes . ▁ ▁Rep lication ▁update ▁strategy ▁There ▁are ▁a ▁number ▁of ▁ways ▁the ▁rep lication ▁management ▁system ▁can ▁handle ▁the ▁updates ▁of ▁rep lic as . ▁The ▁updates ▁may ▁be ▁designed ▁around ▁a ▁central ized ▁model ▁where ▁a ▁single ▁master ▁rep lica ▁updates ▁all ▁others , ▁or ▁a ▁decent ral ized ▁model , ▁where ▁all ▁pe ers ▁update ▁each ▁other . ▁The ▁topology ▁of ▁node ▁pla cement ▁may ▁also ▁influence ▁the ▁updates ▁of ▁rep lic as . ▁If ▁a ▁hierarchy ▁topology ▁is ▁used