In SRND guide I have read that:
Cisco supports the synchronization of up to 60,000 user accounts per cluster, but does not enforce this limit. Synchronizing more than 60,000 user accounts can lead to starvation of disk space, slower database performance, and longer upgrade times.
This limitation (60,000 users), depends on the size of the cluster/platform? I mean, if I have a single server 7825, for instance, can I synchronize it with an LDAP server with 60,000 users??? I doubt it...
It depends on the size of the disk space (hard drive). CUCM pre-allocate the DB space on HDD.
Yes, 7825 can synchronize with 60,000 users. If that's your question.