Vendo como o CentOS é uma ramificação do RHEL, e a documentação do RHEL 7 diz que 50 GB, o CentOS deve ser o mesmo.
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Um trecho:
/home partition - recommended size at least 1 GB
To store user data separately from system data, create a dedicated
partition within a volume group for the /home directory. This partition
should be sized based on the amount of data that will be stored locally,
number of users, and so on. This will enable you to upgrade or reinstall
Red Hat Enterprise Linux without erasing user data files.
If your storage space is bigger than 50 GB, a /home partition will be created
along with other partitions if you select automatic partitioning.