Windows 7 does not support software RAID-5
The software based striped volume with parity (Raid-5) is not supported in Windows 7. However, Windows 7 do support hardware-based RAID using a hardware raid controller. This is by design according to Microsoft Technet Forums and considering that hardware-based RAID performs much better and has additional features, I tend to agree with Microsoft not to overload the system with additional cpu-intensive activity. What I don’t understand is why the option is there but not usable – it’s grayed out! Even, the Diskpart command line tool has a create volume raid option but if you try out, it returns – The command you selected is not available with this version of Windows.
Hardware RAID-5 offers failover protection and performance improvement. RAID-5 writes data in small blocks or stripes on three or more disks simultaneously. A stripe of data across all disks participating in the set consists of the actual data and parity information. Parity information is not stored on the same disk but distributed among the disks. In fact, RAID-5 is sometimes referred to as Striping with Distributed Parity.
The parity information or bit is the result of a computation made on the data in the stripe. The purpose of the parity bit is to recover a missing data block when one disk fails. If one disk from a striped set of three fails, then the missing data can be recomputed from the remaining data blocks and parity information. The process of recovering the missing disk, after the faulty disk is replaced, is known as rebuilding or regenerating the striped set. On the other hand, if two disks fail then you cannot recover the data. To create a RAID-5 set you require at least three disks. However, having more than three disks participating in the stripe set will improve data access performance.
Parity information uses disk space equivalent to a single disk, therefore, if the set is made up of three disks each 500GB in size, then you have 1TB of usable capacity. As a general rule, one disk is used for the parity information – in this case you lose one third of the set. Some additional features of hardware RAID controllers are the support for more disks drives and RAID levels, memory cache with an optional back up battery and better management tools.