PHD quota’s

Hi all. This may have been covered before, and I am sure I have seen something about it. Although for the life of me can not find the information. I am wanting to quota my portable home directories server side. I don't really care about backing up data as such. The reason I have them in place is to keep settings and profiles on the server so when users switch machines they have there settings follow them. Music, photos and personal data is the responsibility of the user. Documents have there place in the server structure. So the only data I really need to back up is the settings. I am sure I saw some were before that I could have a phd from the machine sync into a disk image probably a spares image. This would then enable a quota for me. Is this possible and does any one have a link to the information regarding this? Thanks