DRL log subdisks store the dirty region log of a mirrored volume that has DRL enabled. A volume with DRL has at least one log subdisk; multiple log subdisks can be used to mirror the dirty region log. Each log subdisk is associated with one plex of the volume. Only one log subdisk can exist per plex. If the plex contains only a log subdisk and no data subdisks, that plex is referred to as a log plex.
The log subdisk can also be associated with a regular plex that contains data subdisks. In that case, the log subdisk risks becoming unavailable if the plex must be detached due to the failure of one of its data subdisks.
vxassist command is used to create a dirty region log, it creates a log plex containing a single log subdisk by default. A dirty region log can also be set up manually by creating a log subdisk and associating it with a plex. The plex then contains both a log and data subdisks.