Understanding NFS and CIFS file naming

About file naming conventions in multiprotocol environments

File naming conventions depend on both the network clients' operating systems and the file-sharing protocols. The operating system and the file-sharing protocols determine the

Length of a file name
Characters a file name can use
Case-sensitivity of a file name

Length of file names

Data ONTAP supports the following file name lengths:

Maximum of 255 characters for NFS clients and CIFS clients that support the PC long file name format
Maximum of 8-character file names and 3-character file name extensions for CIFS clients that support the 8.3 format, such as MS-DOS and Windows 3.x clients

Characters a file name can use

If you are sharing a file between clients on different operating systems, you should use characters that are legal to both operating systems. For example, if you use UNIX to create a file, don't use a colon (:) in the file name because the colon is an illegal MS-DOS character. Because restrictions on legal characters vary from one operating system to another, refer to the documentation for your client operating system for more information about prohibited characters.

Case-sensitivity of a file name

File names are case-insensitive, but case-preserving, for CIFS clients and case-sensitive for NFS clients.

For example, if a CIFS client creates Spec.txt, both CIFS and NFS clients display the file name as Spec.txt. If a CIFS user later tries to create spec.txt, the user's application instructs the user to choose another name because, to the CIFS client, that name currently exists. If an NFS user later creates a file named spec.txt, NFS and CIFS clients display the file name differently, as follows:

On NFS clients, you see both file names as they were created, Spec.txt and spec.txt, because file names are case-sensitive.
On CIFS clients, even those that support the PC long file name format, you see Spec.txt and Spec~1.txt. Data ONTAP creates the Spec~1.txt file name to differentiate the two files.

Creating lowercase file names

You can set an option to have all new file names created in lowercase text for better compatibility between 16-bit applications and some UNIX tools. This option is turned on by default, which does not force lowercase file names.

To set lowercase text for all new file names, complete the following step.

Step	Action
1	Enter the following command: options cifs.save_case off

How Data ONTAP creates file names

Data ONTAP creates and maintains two file names for files in any directory that has access from a CIFS client: the original long name and a file name in 8.3 format. Data ONTAP generates an 8.3 format file name as follows:

It truncates the original file name to six characters, if the file name exceeds six characters.
It appends a tilde (~) and a number or letter to the name, to ensure that the file name is unique. If it runs out of letters and numbers because there are too many similar names, it creates a unique file name that bears no relation to the original file name.
It truncates the file name extension to three characters.

Example

If an NFS client creates a file named specifications.html, the 8.3 format file name created by Data ONTAP is specif~1.htm. If this name already exists, Data ONTAP uses a different number at the end of the file name. For example, if the NFS client creates another file named specifications_new.html, the 8.3 format of specifications_new.html is specif~2.htm.