Benefits of Windows Server 2016 ReFS File System

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Windows Server 2016 offers many exciting benefits across the board. However, when thinking about new storage features with this release and more importantly how it affects backups, one updated feature we want to take a closer look at is Windows Server 2016 ReFS file system 3.1. It offers huge improvements over previous file systems in certain use cases as well as predecessor versions of ReFS found in Windows Server 2012. What is ReFS? What are some of the benefits to using Windows Server 2016 ReFS file system and Windows server backup? How does ReFS make a difference in virtualization and backup technology? Are there use cases in which we would not use ReFS?

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What is ReFS File System?

The ReFS file system stands for "Resilient File System" and gets its name from the new resiliency features that are baked into the new file system. Aside from resiliency, the new Microsoft file system is designed with several goals in mind – maximize availability, scalability, and integrity. No longer do administrators have to worry about running the chkdsk utility that detects errors in the file system. This is due in part to ReFS having the ability to perform online checks in real time of the file system health. ReFS uses checksums that allow it to detect any corruption of data and recover from that corruption quickly. In fact, if you look at a ReFS formatted volume and run Tools >> Check on the volume, you will quickly receive a message that "You don’t need to check this drive, The ReFS file system does not need to be checked."

ReFS file system

Windows Server 2016 ReFS Benefits

Two of the use cases where ReFS really shines is in the areas of virtualization and use by modern backup solutions. A few high-level benefits of Windows Server 2016 ReFS file system include:

  • ReFS takes advantage of B+ trees in the file structure. B+ tree is very efficient in storing data as there is a very high fanout of children nodes in the structure. By using pointers, the B+ tree can reduce the amount of I/O operations to retrieve an element in the tree.
  • Maximum volume size for ReFS is 1 Yottabyte or 1 trillion terabytes!
  • File metadata is periodically scrubbed by reading and performing checksum operations on the data. This new scrubber is another mechanism to ensure file resiliency.
  • File integrity streams provide additional file data checksums
    • Interestingly, with the added resiliency benefits, ReFS is the recommended file system for Exchange 2016 database/log locations
  • Windows Server 2016 ReFS introduced block cloning technology – This allows for pointer references to blocks that would otherwise have to be moved around.
    • We will talk more about this below, however, in regards to backups, block cloning in ReFS greatly increases performance of backup solutions that can take advantage of the block cloning technology. Synthetic full backups would no longer need to move data around but rather can utilize the pointers to existing blocks for the synthetic operation.
  • Sparse VDL – Sparse VDL or (Valid Data Length) allows ReFS to zero out files very rapidly. When creating a fixed sized VHD disk in Hyper-V, the operation could take minutes to complete to allocate the disk size. However, with sparse VDL ReFS can zero out the Hyper-V disks files rapidly. It now takes seconds to create a large fixed size disk on ReFS.

Creating the default size 127GB fixed size disk in a Hyper-V cluster with a ReFS clustered shared volume, shown below, took seconds. This operation would have taken minutes on a traditional NTFS formatted volume. So no longer will the time it takes to create fixed size disks be a deterrent to using them.

Creating hard disk in a Hyper-V cluster with a ReFS clustered shared volume

Backup Technology Use Cases

Utilizing ReFS block cloning in modern backup solutions can yield tremendous results. Many legacy backup solutions that backup virtual environments, use a process called synthetic full backups. Before we define a synthetic full backup, let’s think about a traditional full backup. With a traditional active full backup of a virtual machine, we retrieve all needed data for the full backup from the production VMware or Hyper-V virtual machine itself. In doing that, we are essentially hitting both the production network and storage to create that full backup. With synthetic backups, the data for the full backup is synthesized from backup data that you already have in your backup repository. New full backups are synthesized and the backup chain is moved forward. Block cloning technology with Windows Server 2016 ReFS can greatly speed up the process in which legacy backup solutions can synthesize backups due to the movement of pointers rather than the blocks themselves.

With modern backup solutions such as Nakivo Backup & Replication, this is not required, though. VM backups are stored in the full synthetic mode. Each recovery point is aware of the blocks that are needed to fully recover a virtual machine. This means there is no need to run the transformation of backup files or recreate full backups using the synthetic process.

When Not to Use Windows Server 2016 ReFS

While ReFS 3.1 is certainly a remarkable file system bringing forth many improvements, are there use cases where we do not use ReFS? Yes – Below are a few areas to note:

  • ReFS cannot be used for the system drive/boot drive of the Windows operating system. In fact, you will not see an option to format your boot drive with ReFS during Windows installation as NTFS is still the way to go for the operating system.
  • ReFS does not support Windows Deduplication, so if you want to utilize deduplication for a Windows volume by using the native Windows deduplication capability, you will need to stick with NTFS.
  • ReFS does not support file level encryption. You can use BitLocker encryption with ReFS, however, this is a volume level encryption technology. If you want to encrypt at the file/folder level, again, you will need to use NTFS.
  • Disk Quotas – Disk Quotas are not supported with ReFS.


The new features included in Windows Server 2016 ReFS will greatly benefit environments with the resiliency, scalability, and performance improvements it brings to the table. Microsoft has no doubt created the file system that will pave the way forward in future Windows releases. We can be sure that additional missing features that are still only found in NTFS will be added in upcoming versions of ReFS.

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