What is ReFS?
Microsoft introduced ReFS with Windows Server 2012. It was designed to detect and repair corruption on its own and to scale to very large volumes, not to replace NTFS everywhere. NTFS is still the file system for the Windows system drive; ReFS is not used as the boot volume. ReFS is mostly found on servers holding virtual machines, backups, and other large data sets.
Key features
- Checksums. ReFS keeps checksums for its metadata and can also keep them for file data, a feature called integrity streams. Every read can be checked against the checksum to catch silent corruption.
- Automatic repair with Storage Spaces. On a mirrored or parity Storage Space, when ReFS finds a block that fails its checksum, it reads the good copy and repairs the bad one while the volume stays online.
- Background scrubbing. A scheduled integrity scanner reads data periodically, so corruption is found before anyone needs that data.
- Online repair. ReFS isolates and repairs damage without taking the volume offline. It does not use
chkdsk, which is an NTFS and FAT tool. - Safer metadata updates. ReFS writes changed metadata to a new location instead of overwriting it in place, which reduces the risk of corruption from a power loss during a write.
- Scale. ReFS is built for multi-petabyte volumes and very large files.
- Virtualization performance. Block cloning and related features speed up Hyper-V operations such as merging checkpoints and creating fixed-size virtual disks, and backup software uses block cloning as well.
What ReFS does not do that NTFS does
- Windows does not boot from a ReFS volume.
- No Encrypting File System (EFS). BitLocker volume encryption does work on ReFS.
- No NTFS disk quotas.
- No 8.3 short file names.
- It is not supported on removable media such as USB flash drives.
- There is no in-place conversion from NTFS. Moving to ReFS means formatting a volume and copying the data over.
Where ReFS is available
- Windows Server, from 2012 on, for data volumes, Storage Spaces and Storage Spaces Direct, Hyper-V virtual machine storage, and backup targets.
- Windows client: creating ReFS volumes is limited to editions such as Windows Pro for Workstations and Enterprise.
- Dev Drive: the Windows 11 Dev Drive feature creates a ReFS-formatted volume tuned for developer workloads such as source code and package caches.
- macOS and Linux do not include native ReFS support.
ReFS vs. NTFS at a glance
| Feature | NTFS | ReFS |
|---|---|---|
| Windows boot volume | Yes | No |
| Data checksums and self-repair | No | Yes, with integrity streams and Storage Spaces |
| EFS file encryption | Yes | No |
| Disk quotas | Yes | No |
| Typical use | System drives, general use | Servers, VM storage, backup repositories |
ReFS on the CompTIA A+ exam
ReFS is on the Core 1 acronym list as Resilient File System. Comparing file systems is Core 2 material, alongside NTFS, FAT32, exFAT, ext4, XFS, and APFS, which also appear on the acronym list. Know that ReFS is a Microsoft file system focused on integrity and large volumes, that it pairs with Storage Spaces for self-healing, that it is mainly a server file system, and that it is not used for the Windows boot drive. If a question asks for a Microsoft file system designed for resiliency against data corruption on large server volumes, the answer is ReFS; if it asks what the Windows system drive uses, the answer is NTFS.