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I am running a server with SQL server with 2 x 960GB NVME Datacenter SSD in RAID1, windows files and database and default database files on the same disk.

This server is using the default format allocation size 4Kb.

I have read that 64Kb is better for SQL and this server is only hosting SQL server.

Should I reformat the server and reinstall Windows 2019 server with 64Kb allocation size ?

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    May be not a big deal on that kind of storage. However, why databases are on system disk? I’m much more concerned by this than the allocation unit size Commented Nov 28, 2021 at 14:18
  • Well, you are correct. I was thinking to just make 1 big disk and have everything on it. but I will create a partition for the OS with 4k and partition for db with 64k. Commented Nov 29, 2021 at 11:23

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Should I reformat the server and reinstall Windows 2019 server with 64Kb allocation size ?

The cluster size is one part of the equation, though in reality for NVMe it's going to be moot. I wouldn't expect any statistically significant performance difference with modern OS's and hardware. Really where this is going to bite you is in the FRS record size (NTFS metadata if using NTFS) as with a 4k cluster and if defaulted to using the 1k FRS then you're more likely to hit OS error 665 than you would with 64k cluster sizes, however using NTFS means it's not if it will happen but when it'll happen.

Long and short is it won't make much if any difference and the real issue is to not hit a 665 error.

665:

The requested operation could not be completed due to a file system limitation

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