Totally normal behaviour.
md0, md1, md2 etc. are all read-only virtual Memory Disks.
% mdconfig -l -u 0
md0 malloc 20M
# malloc type is used for UTM.
% mdconfig -l -u 1
md1 vnode 1.4G /cf/packages/junos
# vnode type
% mdconfig -l -u 2
md2 swap 1.0G
# this is swap for when the system is under memory pressure.
etc.
Whereas the partition /cf/var is used to store logs, cores, temporary packages etc. This is typically the partition that you need to free up space on when an upgrade fails due to lack of free space.
Regards,