This post will help you with a few ESX commands that you can run from ESX console to find out details of storage connected to ESX host. ESX/ESXi can have multiple types of storage like locally connected storage, SAN, NFS, or USB. If you want to find out the size and other details of these storage, then you can use the below command based on your ESX version.
On ESXi 5.x
esxcli storage core device list
This will list all the storage devices attached to a ESX host. The size parameter for each storage drive gives you the storage size in MB.
On ESX/ESXi 4.x
This will list all the storage devices attached to a ESX/ESXi4.x host. The size parameter for each storage drive gives you the storage size in MB.
I found some more useful commands while searching for this. You may find these useful.
esxcli storage core path list
Generates list of LUN paths that are connected to ESX host. You will find storage device IDs, displayname, and several other information that you generally see in storage section of ESX Configuration tab in VC.
esxcli storage vmfs extent list
Provides list of extents and their details connected to ESX server.
You can refer to http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1014953 for some more useful commands.