Local Cache Buffer Access Ratio - percentage of blocks satisfied from local cache to the total number of blocks requested by sessions. In OLTP applications it is desirable to maintain this ratio as high as possible because this is the least expensive and fastest way to get the database block.
This ration is calculcated as:
Local Cache Buffer Access Ratio = 1 - ( physical reads cache + Global Cache blocks received ) / Logical Reads
Note. Please note, that this ratio has exactly same definition and meaning as the Buffer Hit Ratio for non-RAC instance.