I found this host I am checking has an usb key...... so is it OK to say my ESXi boot from USB Key according to this
~ # ls -l /
lrwxrwxrwx 1 root root 49 May 24 00:05 altbootbank -> /vmfs/volumes/ef6eb276-b4cfb6ea-62cb-b61118474298
drwxr-xr-x 1 root root 512 Apr 25 17:59 bin
lrwxrwxrwx 1 root root 49 May 24 00:05 bootbank -> /vmfs/volumes/4a75ec7b-113aa22c-eaa4-44993d3d652c
-r--r--r-- 1 root root 300059 Aug 2 2012 bootpart.gz
....
-r-x------ 1 root root 21806 Apr 25 17:54 local.tgz
lrwxrwxrwx 1 root root 6 Apr 25 18:00 locker -> /store
...
lrwxrwxrwx 1 root root 22 Apr 25 18:00 productLocker -> /locker/packages/5.1.0
drwxr-xr-x 1 root root 512 Apr 25 18:00 sbin
lrwxrwxrwx 1 root root 49 Apr 25 18:00 scratch -> /vmfs/volumes/517746dc-d86f6bd4-d1e1-5cf3fc1bda9c
lrwxrwxrwx 1 root root 49 May 24 00:05 store -> /vmfs/volumes/517746d1-079d99d4-0caf-5cf3fc1bda9c
...
~ # df -h
Filesystem Size Used Available Use% Mounted on
.......
vfat 4.0G 17.1M 4.0G 0% /vmfs/volumes/517746dc-d86f6bd4-d1e1-5cf3fc1bda9c
vfat 249.7M 130.2M 119.6M 52% /vmfs/volumes/ef6eb276-b4cfb6ea-62cb-b61118474298
vfat 249.7M 144.8M 104.9M 58% /vmfs/volumes/4a75ec7b-113aa22c-eaa4-44993d3d652c
vfat 285.8M 201.9M 83.9M 71% /vmfs/volumes/517746d1-079d99d4-0caf-5cf3fc1bda9c