It’s been many years since I read that SQL databases should use an NTFS volume formatted with at 64KB file allocation unit size (block size). So long that I didn’t remember why or if it is still considered best/good practice. It appears that it is according to Microsoft and the foremost authority on SQL with ConfigMgr.

Microsoft recommends this for User Databases and the TempDB: https://docs.microsoft.com/en-gb/azure/virtual-machines/virtual-machines-windows-sql-performance?toc=%2fazure%2fvirtual-machines%2fwindows%2ftoc.json

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Steve Thompson [MVP]: https://stevethompsonmvp.wordpress.com/2014/07/25/sql-server-ntfs-cluster-size

Steve explains, “The reason that SQL Server prefers 64KB NTFS cluster size, this happens to correspond to the way SQL Server allocates storage. One page = 8K, and SQL Server allocates an Extent, which is 8 pages in size. 8 pages x 8KB = 64KB/extent.”

To check the Block Size per drive/volume/partition…

From PowerShell, execute

Get-WmiObject -Namespace 'root\CIMv2' -Class Win32_Volume -Filter "DriveType = 3 and Label <> 'Recovery'" | Select Name, Label, BlockSize

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OR from a Command Prompt

fsutil fsinfo ntfsinfo s:| findstr "Bytes per"

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OR create a small file on the drive(s) and check it’s properties.  This can easily be done by…

  • open Notepad, hold any key for about 30 seconds, then save the file
  • open a Command Prompt and type FOR /L %I (1,1,200) DO @echo %I>> %temp%\test.file  (or similar)

Using Windows Explorer, right-click the test file and notice the Size and Size on Disk info.

From testing, the file had to be more than 500 bytes on a 4K block size volume to register any size on the disk.  On the 64K block size disk it took about 800 bytes to register.  You mileage may vary though.

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In addition, if the SQL PowerShell module installed or there is some other method to query the existing SQL server, PowerShell can check if the block size on all drives where a SQL files exist or will exist if using the default file locations.

Import-Module SQLPS
$SQLDrivesInUse = @(Invoke-Sqlcmd -Query 'SELECT DISTINCT left(physical_name,3) [Drive] from master.sys.master_files')
Write-Output 'SQL Drives In Use'
$SQLDrivesInUse | Format-Table -AutoSize

$SQLDriveDefaults = @(Invoke-Sqlcmd -Query "SELECT Left(Convert(varchar(255), SERVERPROPERTY('instancedefaultdatapath')),3) [Drive] UNION SELECT Left(Convert(varchar(255), SERVERPROPERTY('instancedefaultlogpath')),3)")
Write-Output 'SQL Drive Defaults'
$SQLDriveDefaults | Format-Table -AutoSize

$DiskDrives = @(Get-WmiObject -Namespace 'root\CIMv2' -Class Win32_Volume -Filter "DriveType = 3 and Label <> 'Recovery'" | Select Name, Label, BlockSize, ExpectedBlockSize, IsOK)

ForEach ($DiskDrive in $DiskDrives) {
    $SQLDrivesInUse.Drive | ForEach-Object {
        If ($_ -eq $DiskDrive.Name) { $DiskDrive.ExpectedBlockSize = 8*8*1024 }
    }
    $SQLDriveDefaults.Drive | ForEach-Object {
        If ($_ -eq $DiskDrive.Name) { $DiskDrive.ExpectedBlockSize = 8*8*1024 }
    }

    If ($DiskDrive.ExpectedBlockSize -eq $null) {
        $DiskDrive.ExpectedBlockSize = 4*1024
    }
   
    If ($DiskDrive.BlockSize -eq $DiskDrive.ExpectedBlockSize) {
        $DiskDrive.IsOK = $true
    } else {
        $DiskDrive.IsOK = $false
    }
}
$DiskDrives | Select Name, Label, BlockSize, ExpectedBlockSize, IsOK | Format-Table -AutoSize

 

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ConfigMgr and SQL – NTFS allocation unit size
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