cant use full disk space

Hi, i am new drobo 5n user, have installed 5-6 terabit drives but it wont let me use 5.26 terabits, it just says unused. help I have win7 ultimate

do you have a bit more information you can help provide?

such as how many drives did you install, and was each one how many TB?
and if you look in dashboard software does it show you if you are using Single Drive SDR or Dual Drive redundancy DDR?

a simple rule for SDR is this:
total space available for your data is:
Each Drives TB capacity added together,
take away your largest drives capacity TB
and multiply the remaining number by 0.9