disk problem when turning on/off the storage

Hi

I have created 2 disks same size 2G one dynamic and one fixed , I connected them to my windows machine and was able to access them Read/Write) using the server manager I turned off the storage and then the windows machine, and turn on the storage and the windows when I turned on the machine the size of the two disks become 4096K and all the data is gone. Any suggestion how can I prevent this from happen again?

Thanks