Your client application if; writing data to a Region. By default, where is the data saved first?

A.
StoreFile

B.
WAL

C.
MemStore

D.
Local disk on the RegionServer

Explanation:
HBase data updates are stored in a place in memory called memstore for fast write.
In the event of a region server failure, the contents of the memstore are lost because they have
not been saved to disk yet.
Reference:HBase data updates are stored in a place in memory called memstore for fast write. In
the event of a region server failure, the contents of the memstore are lost because they have not
been saved to disk yet.
http://www.cloudera.com/blog/2012/07/hbase-log-splitting/(Log splitting, first paragraph)