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2 GB RAM available minimum; 4 GB RAM or more available recommended.
Note: Your SEPM server may require additional RAM depending on the RAM requirements of other applications that are already installed.
Refer this article to find more info about System requirements:
System Requirements for Symantec Endpoint Protection, Enterprise and Small Business Editions, and Network Access Control 12.1.4.1/12.1.4.1a
http://www.symantec.com/docs/TECH216260
The Symantec Endpoint Protection Manager (SEPM) 11.x recovery file is a text file that is compiled manually by the administrator during preparation for the possible need of disaster recovery. It is not possible to directly restore an 11.0 backup on a 12.1 system - the recommended steps are to restore on a new 11.0 SEPM install, then upgrade to 12.1
Refer this article: Failure when using 11.x disaster recovery files with Symantec Endpoint Protection Manager 12.1
http://www.symantec.com/docs/TECH162071
Total how many clients are in the network? Upgrade process is very straight forward. Check this article
https://www-secure.symantec.com/connect/articles/sep-11x-sep-121-upgrade-process-graphical-overview
If you have done a fresh install then restore the communication using available options.
Refer these articles.
https://www-secure.symantec.com/connect/articles/sep-121-ru2-and-reset-client-communication
http://www.symantec.com/docs/HOWTO80762