Do you mean by default (without reconfiguring the sandbox)? It looks like the sandbox (HDP 2.5) is configured with 42.4GB of space. A fair amount (over half) is already taken so there is under 20GB of available space.
If you mean with reconfiguration of the underlying vm, then (at least on the vm image I am using under vmware) the virtual drive maxes out at 2TB (2040GB).
@wzheng , This sounds like a question preparatory to using it in production. The sandbox really is mostly set up for single-node single-user exploration. However, our cloud offerings are intended for production use, and are available for HDP on your choice of AWS, Azure, and GCP; see https://docs.hortonworks.com/HDPDocuments/Cloudbreak/Cloudbreak-1.6.3/index.html