ReFS
next-generation Microsoft file system
Resilient File System (ReFS), codenamed "Protogon", is a Microsoft proprietary file system introduced with Windows Server 2012 with the intent of becoming the "next generation" file system after NTFS.
ReFS was designed to overcome problems that had become significant over the years since NTFS was conceived, relating to changes in data storage requirements. These requirements arose from two major changes in storage systems and usage (the size of storage in use large or massive arrays of multi-terabyte drives now common), and the need for continual reliability. As a result, the file system needs to be self-repairing (to prevent disk checking from being impractically slow or disruptive), along with abstraction or virtualization between physical disks and logical volumes.
The key design advantages of ReFS include automatic integrity checking and data scrubbing, elimination of the need for running chkdsk, protection against data degradation, built-in handling of hard disk drive failure and redundancy, integration of RAID functionality, a switch to copy/allocate on write for data and metadata updates, handling of very long paths and filenames, and storage virtualization and pooling, including almost arbitrarily sized logical volumes (unrelated to the physical sizes of the used drives).
Comparison with NTFS
Major new features
Improved reliability for on-disk structures
ReFS uses B+ trees for all on-disk structures, including all metadata and file data. Metadata and file data are organized into tables similar to a relational database. The file size, number of files in a folder, total volume size, and number of folders in a volume are limited by 64-bit numbers; as a result, in practice ReFS supports a maximum file size of 35 petabytes, and a maximum volume size of 35 petabytes.
The theoretical maximum is way beyond that however not even Windows supports ReFS volumes with the full theoretical limits. The design allows for a theoretical maximum of a single volume of 2^78 bytes with 16KB cluster size (2^64 * 16 * 2^10) with a maximum of 2^64-1 bytes for a single file. That maximum volume size is currently soft limited by Windows’ stack addressing being limited to 2^64 bytes; a maximum path length of 32K (soft limited to 255 unicode characters on Windows to align with NTFS and because of restrictions in some older APIs for handling file paths); a maximum of 2^64 directories on a single volume; 2^64 files per directory; a single storage pool is limited to a maximum of 4 PB. It as well as all other filesystems supported by Windows are defined within the Open Specification.
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