Hello,
Storage Spaces is a technology in Windows and Windows Server that can help protect your data from drive failures. It is conceptually similar to RAID, implemented in software. You can use Storage Spaces to group three or more drives together into a storage pool and then use capacity from that pool to create Storage Spaces. These typically store extra copies of your data so if one of your drives fails, you still have an intact copy of your data. If you run low on capacity, just add more drives to the storage pool.
In setting up a storage space, it's recommended that you use a hard drive that doesn't contain important files as the drive will be formatted to mirror the host drive.
For more information regarding Storage Spaces, read this FAQ page.
Hope the information I provided helps.