I have used Consistent hashing algorithm^[1]. The lost keys are 1/n of the total number of keys. This means the successful key fetch will be 6/7 *100 around 85%.
Please download this repository and run the following command. I found this blog (http://michaelnielsen.org/blog/consistent-hashing/) very informative for implementing consistent hash, I tailored the available code to solve the assignment.

$ [sudo] python mamcache_client.py

Reference for consistent-hashing code :
_{[1] Michael Nielsen's blog, http://michaelnielsen.org/blog/consistent-hashing/}