The distinction between persona and personality is a subtle one, but I understand it to be the one that Mira makes here - a persona is a mask (literally something sounded through) that we adopt. I have a persona as a teacher, and was specifically taught to create one on my PGCE, through adopting certain behaviours - "don't smile until Christmas" is one that particularly springs to mind. My identity as a teacher is informed by much more than my persona, it's the way I view myself in that role, the values I bring to it, how well I perform in that role and (as Mira mentions) the responsibilities I feel. Those identities change from role to role in my life, and those different identities (in combination with how much caffeine I've drunk, how much sleep I've had and so on) will mean I display different aspects of my personality in different roles and at different times. I see moving from offline to online, and through different online identities as just an extension of this process we do all the time.