[CentOS] redundant networked secure file system recommendation

Hi all,

We are currently running a NFS-based server centric setup. I would
like to set up something where I can easily have more than one
redundant server, security/authentication (this part seems a little
flaky with NFS, at least did several years ago), with the capability
to easily add/remove servers as necessary, take redundant servers down
for maintenance, etc. Total volume we expect to run on the server side
will be somewhere between 10-30 TB. The servers will most likely be
CentOS machines, the clients mostly Linux machines with some Macs and
possibly Windows (the latter part not that important).

Any insight, thoughts and recommendations will be much appreciated.

Thanks.

Boris.