Encrypt file systems ?
For a run of the mill office server, encrypting the important file systems should not really slow it down too much. A quick search finds: Ubuntu extra overhead of 5%, others should not be vastly different. Thus acceptable on a modern server that has more CPUs/cores that you know what to do with.
If you are smart: do not encrypt the file systems needed to get it up & running, then on a reboot you can ssh in and get the encrypted file systems mounted.