Did you do a package install (.deb?) or you downloaded the tar?
If the latest, you have to adjust the limits.conf file (/etc/security/limits.conf) to raise the nofile (number of files open) for the cassandra user.
If you are using the .deb package, the limit is already raised to 100 000 files. (can be found in /etc/init.d/cassandra, FD_LIMIT).
However, with the 2.0.x I had to raise it to 1 000 000 because 100 000 was too low.
I have experimenting cassandra latest version for storing the huge the in our application.
Write are doing good. but when comes to reads i have obsereved that cassandra is getting into too many open files issues. When i check the logs its not able to open the cassandra data files any more before of the file descriptors limits.
Can some one suggest me what i am going wrong what could be issues which causing the read operating leads to Too many open files issue.