I am beginner too. But I found the answer to your second question. It is about 'SAS Views'.

SAS Views provide all the functionality and flexibility of SAS data sets,    but occupy only a minuscule fraction of the space of a full SAS data set. The View acts as sort of a "map" to the source data, instead of making a complete copy of it in SAS data format.
SAS Views are documented in the SAS OnlineDoc(tm).

To create a SAS View, add the VIEW= option to the DATA statement. The SAS data view name provided after VIEW= must be the same as at least one of the SAS data set names mentioned in the DATA step statements, but may not be the same as a SAS View or SAS data set already in the same library. Virtually all the language of the DATA step is the same as it would be if a true SAS data set were being created, except that the VIEW= option is added. For example, the following statements read raw data and create a SAS View called view1.ssv01:

            libname viewout '~/sasviews';
            filename raw1 '~/rawdata/file1.raw';

            data viewout.test1 / view=viewout.test1;
              infile raw1;
              input var1 var2 var3;
            run;
      Later, all that is needed to access the data with a PROC are the global statements (LIBNAME, FILENAME) and the PROC itself. For example,

            libname viewout '~/sasviews';
            filename raw1 '~/rawdata/file1.raw';
            proc print data=viewout.test1;

Views can be used to access other SAS data sets, allowing the use of subsets without wasteful usage of space. Imagine you have a master SAS data set, and routinely you need to process subsets of the data. Instead of storing potentially redundant subsets in the form of SAS data sets, Views could be used to save space. Consider the following:

            libname allsas '~/sasdata';
            libname viewstor '~/sasviews';
            data viewstor.females / view=viewstor.females;
                set allsas.master;
                if sex='f';
               
            data viewstor.males / view=viewstor.males;
                set allsas.master; if sex='m';

This would allow you the functionality of two subsets in addition to the master data set, while using only a tiny bit more disk space than the master data set itself. If real SAS data sets were used for the subsets, together they would have doubled the amount of disk space used.

To the first one, please refer to SAS support file:
http://www.sas.com/offices/NA/canada/downloads/presentations/Vancouver_Fall_2005/SAS_Efficiency_considerations.pdf

The BUFSIZE = system option or data set option to control the page size of an output SAS data set. The BUFNO= system option or data set option to control the number of SAS buffers open simultaneously in memory. You can get more details from the above link and SAS website.




Hope it helps

SAS support file