I run ReFS in two configurations:

  • In a storage spaces mirror (2x4TB), for most valuable data
  • Standalone on a single disk, for offsite backups (NB: not my only backup)

In both of these configurations the data integrity features have been enabled in ReFS / Storage Spaces.

I run the Windows defragmentation tool monthly. However I ran defraggler straight after the windows defrag tool recently and it reported significant fragmentation, with some files having thousands of fragments. Defraggler can defragment the disk, but it's very slow - 2TB of data can take 16 - 24 hours. Is fragmentation a problem in ReFS?


  • The "problem" is: ReFS disks have significant fragmentation
  • The question: should I defragment these disks using defraggler, to remove all fragmentation, or let the Windows defrag tool do whatever it thinks is required?

1 Answer 1


There doesn't seem to be a definitive answer to the question as I myself have been looking for an answer.

One thing to note is that the inbuilt defragmentation software in Windows Server 2012 and 2016 both support and report on ReFS storage health.

I don't have any ReFS volumes that have been used over an extended period of time and all are still reporting a status of "OK". Standard Windows defragmentation is enabled on systems running ReFS.

I would presume that disabling defragmentation of ReFS drives would cause the their performance to degrade and in turn cause a status of "OK" to change to "Needs defragmentation". That leads me to believe that ReFS drives should be defragmented to maintain performance during the lifespan of the storage device.

Exactly how often or how aggressively is another matter entirely and that would depend on how the storage is used.

With regards to software: We use PerfectDisk Server and haven't noticed it using too much time defraging an ReFS volume, but we have only tested on a file server with little over 1TB of data.

  • I was reading this post: windowsitpro.com/windows-server-2012/… Nov 10, 2016 at 9:07
  • Can't seem to edit comment. Continuing on, take notice of the last paragraph: "Note also that ReFS only uses a 64KB cluster size, which means a lot of wasted space for disks with lots of small files. Since ReFS uses a Copy on Write mechanism, there's a greater chance of fragmentation." Nov 10, 2016 at 9:08
  • If anyone is interested: Drive Size: 3TB Nov 13, 2016 at 21:58
  • Gotta stop hitting enter and commenting before I'm done writing! COntinuing on... Volume: REFS UsedSpace: 2.3TB Software: PerfectDisk 14 Server Time to defrag entire volume: 44:40:10 (HH:MM:SS) Nov 13, 2016 at 22:01

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