Resilient File System, also known as ReFS is a new file system introduced in Windows Server 2012. The main purpose of this new file system is to be resilient against data corruption while providing data availability. This new file system target earlier adopters that want a foundation for future improvements. ReFS allows IT admins to implement cost effective infrastructure for scalable and available data using off the shelve storage devices.
ReFS works by distributing files across multiple disks and protects files from partial disk failures. ReFS file system is designed in mind by assuming customers will be using unreliable storage such as consumer class SATA drives. Note that ReFS is fully compatible with “legacy” NTFS file system.
ReFS retain data in a particular way that it allows protection from common system errors that can usually cause data loss. When using ReFS on mirrored storage space and detected corruption is enabled on metadata and user data, it can magically repair files using alternate copies. This file system essentially replaces the older mirrored and stripped dynamic disk. ReFS is designed to make data availability priority. ReFS allows instant repair of local corruption without taking the volume offline.
If an administrator chooses not to implement mirror storage spaces, ReFS uses salvage feature to remove corrupt from the volume while it’s online. Other high availability options for storage spaces are described below.
Two way mirror
Windows Server 2012 will store two copies of the data across two physical drives. If one of your drives fails on the server, it will simply repair from the second copy.
Three way mirror
Windows Server 2012 will store three copies of your data across three physical drives. If one or two of your drives fails on the server, it will repair it from surviving copy.
Windows Server 2012 stores parity information with the data, protecting you from a drive failure. Parity uses drive space more efficiently than mirroring, just like RAID5 but IO is slower. IMO, this is Microsoft implementation of RAID5.
You will notice that you cannot use chkdsk with ReFS. You can use the integrity tool to manage integrity streams.