The HRegionServer opens the region and creates a corresponding HRegion object. When
the HRegion is opened it sets up a Store instance for each HColumnFamily for every table
as defined by the user beforehand. Each Store instance can, in turn, have one or more
StoreFile instances, which are lightweight wrappers around the actual storage file
called HFile. A Store also has a MemStore, and the HRegionServer a shared HLog in-stance。
hbase table中每个列簇都对应着region中的一个store，
1个region对应1个store
1个store对应多个storefile
在hdfs系统中则对应着一个目录，如果列簇中尚无数据，怎该目录为空，也就是该store下还没有storefile。