We have one client that tried disk encryption on their database, it did introduce significant delay with unpredictable sessions of inaccessibility of a few seconds each time. Vicidial was basically unusable for them under that scenario.
As for PCI compliance, full disk encryption is NOT a requirement, but there are a lot of other requirements, depending on the size of your business and how many credit card transactions you process.
On our hosted service, we do offer encrypted custom fields for VICIdial, where the data is stored as encrypted in the database(not using MySQL encryption), But it is not a part of the public VICIdial codebase,
http://www.vicihost.com/?p=131Another option is to use native MySQL encryption to only encrypt the fields that need to be protected,
https://dev.mysql.com/doc/refman/5.5/en ... tions.html