vxvm vxprint output

Hi experts , please see the following output:

v  log-alarm    -            ENABLED  ACTIVE   8388608  SELECT    -        fsgen
pl log-alarm-01 log-alarm    ENABLED  ACTIVE   8388608  CONCAT    -        RW
sd SUN6140-1_1-02 log-alarm-01 SUN6140-1_1 1048576 8388608 0      SUN6140-1_1 ENA
pl log-alarm-02 log-alarm    ENABLED  ACTIVE   8388608  CONCAT    -        RW
sd SUN6140-0_0-01 log-alarm-02 SUN6140-0_0 0   8388608  0         SUN6140-0_0 ENA
pl log-alarm-03 log-alarm    ENABLED  ACTIVE   LOGONLY  CONCAT    -        RW
sd SUN6140-1_1-04 log-alarm-03 SUN6140-1_1 9437712 528  LOG       SUN6140-1_1 ENA

is this a volume with 3 mirrors ?

I noticed that the third Plex , is "LOGONLY" .

could anyone explain this output ? Thanks a lot in adavnce !