Hi,
Could you please update with currently installed exact version.
1) I have only 16GB free space available. SYMC DB size is 8GB. In best practise document, it is recommended to have at least 3 times the space of database size. Now what should I do, there is no chance to have more free space in C: partition.
---> The SEP 12.1 SEPM upgrade installer requires three times the current database size (sem5.db) if upgrading from pre-12.1 SEPM with the embedded database only.
In your case you would required 24GB free space minimum.
If C drive doesn't have sufficient disk space then I would suggest create a sufficient disk space first.
2) Upgrade is smooth or I may end in a disaster?
--> Upgrade process will be very similar as per the following article
https://www-secure.symantec.com/connect/articles/sep-11x-sep-121-upgrade-process-graphical-overview
Please update us with the following details so we can suggest best option to go further:
1) Total Number of SEPM's
2) Total number of SEP clients
3) Total sites if there are any
4) Remote branches if there any, GUP's