The building block of a Coda file system is the volume. A volume is something like a virtual partition. It may exist physically on one server, or it may have several identical copies on two or more servers. It must be mounted cell-wide if it is to be read or written, but it can be backed up without being mounted. Quota is managed by setting a limit on each volume. A volume may have no quota set, in which case it can grow until one of the physical partitions where it lives fills up.
Coda does something to volumes called cloning, which we need to look at more closely. Also there are several different kinds of volume.