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What cluster size does SnapDrive for Windows use when formatting a virtual disk with NTFS?

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Applies to

  • Data ONTAP 7 and earlier
  • SnapDrive 4.1 for Windows
  • SnapDrive 4.2 for Windows

Answer

How can I determine what cluster size SnapDrive for Windows will use when formatting an NTFS file system on a NetApp virtual disk or Logical Unit (LUN)?

SnapDrive only formats using Microsoft NTFS and it utilizes the default format cluster size that is used by Windows Disk Management. This default value is determined by the size of the disk. The following table describes the default cluster sizes for Windows 2000 file system volumes:

Volume size NTFS cluster size
7 MB - 16 megabyte (MB) 512 bytes
17 MB - 32 MB 512 bytes
33 MB - 64 MB 512 bytes
65 MB - 128 MB 512 bytes
129 MB - 256 MB 512 bytes
257 MB - 512 MB 512 bytes
513 MB - 1,024 MB 1 KB
1,025 MB - 2 gigabyte (GB) 2 KB
2 GB - 4 GB 4 KB
4 GB - 8 GB 4 KB
8 GB - 16 GB 4 KB
16 GB - 32 GB 4 KB
32 GB - 2 TB 4 KB

The following table describes the default NTFS cluster sizes for Windows Server 2003 file system volumes:

Volume size NTFS cluster size
7 MB - 512 MB 512 bytes
513 MB - 1,024 MB 1 KB
1,025 MB - 2 GB 2 KB
2 GB - 2 TB 4 KB

If the disk is already formatted, you can use chkdsk in READ_ONLY mode to determine the cluster size. It will be expressed in the bytes in each allocation unit field:

:/> chkdsk x

In the example above, x is the drive in question.

There are 4096 bytes in each allocation unit. This indicates that a 4 kilobyte cluster size is in use.

Note: SnapDrive does not select the cluster sizes. Windows Disk MGMT does this and it chooses the default for the size of the virtual disk. For information regarding different versions of Windows, please contact Microsoft.

Additional Information

Related Link:

Microsoft article: Default cluster size for FAT and NTFS