Hi Jeon,
if I get your question correctly, the closest to df -h is Misha's show file system
VX#show file systems  File Systems:          Size(Mb)      Free(Mb)  Use%    Type  Prefix              68            59    13   flash  nvram:            7697          7146     7   flash  flash:           22282         20574     7       -  vmsdb:           22282         20574     7   flash  internal (/vms) 
However, Watanabe has also a good point listing available space by service show info
VX#service show info
7.0G out of 7.5G available for logs.
20.1G out of 21.8G available for history.
7.0G out of 7.5G available for crashinfo.
List of Files:
acct_server-initd.log                   5.2K    Aug 21 10:58
acct_server.log                         2.7K    Aug 21 10:58  So having this you can notice that flash: partition is mounted for logs and crash-info but rest (database, upgrade files etc) is stored within /internal.
Regards,
Ondrej