Datastore reside on Arcgis server machine, have SQL server connection information.
Data store is between Arcgis server and SQL server. Data store provide arcgis server connection info let arcgis server could get data directly from SQL server. Without datastore, Arcgis server can't connect, can't get data from SQL server.
Data store not only playing connection broker role, also, data store as its name means, it can acturally store the real data for arcgis server use. If you publish data from local file geodatabase, local shape file, these data will be copied to data store on arcgis server. So arcgis server will get these data from data store when a user click a map ask for a piece of data.
Sometimes, SQL server data can be copied to data store instead of retrieve live.from SQL server.
To create SQL server based data store by provide sql server connection info
a new data store created
SQL server SDE connection file's authentication type must match your data store's connection authentication type.
Otherwise, when you publish a layer, if only copied all data from sql server to datastore instead of reference SQL server live data.
Here is SQL server SDE connection, authentication mode is windows authen
data store on arcgis server, its authentication also must be windows authen.
