Old SFTP clients regard / (slash) as a directory separator, which requires the SFTP server to use some "tricks" to fool the clients. The SFTP client generally does not have any inherent knowledge of MVS datasets and accesses all files as they were part of a hierarchical file system.

If an SFTP client tries to open the file //FILE.NAME, the MVS dataset is actually opened. Some SFTP clients remove all consecutive slashes so that the file to be accessed becomes /FILE.NAME. The SFTP server will interpret this as the HFS file FILE.NAME, located at the HFS root. To avoid this client behavior, the SFTP server has other ways of naming MVS datasets. If a client tries to access the file /_FILE.NAME, /FTADV:X=BIN/_/FILE.NAME or /FTADV:X=BIN/__FILE.NAME, the SFTP server interprets these as the dataset //FILE.NAME. All these combinations are needed as it may be necessary to make the SFTP clients pass the correct file or dataset name to the server.

In z/OS, if a dataset name is not enclosed in single quotes, the user prefix is added in front of the dataset name. For example, if user USER1 has a dataset DATASET.NAME1, the user can access it using the dataset name //DATASET.NAME1. It is also possible to use an absolute prefixed name //'USER1.DATASET.NAME1'.

Because single quotes are special characters in most environments, the SFTP server introduces a new convention to use triple slashes to access absolute prefixed dataset names. The name becomes ///USER1.DATASET.NAME1. All combinations of slashes and underscores can be used. For example, USER1 can access his/her dataset using one of the following names:

//DATASET.NAME1
/_DATASET.NAME1
/FTADV:X=BIN/_/DATASET.NAME1
/FTADV:X=BIN/__DATASET.NAME1

or

//'USER1.DATASET.NAME1'
/_'USER1.DATASET.NAME1'
/FTADV:X=BIN/_/'USER1.DATASET.NAME1'
/FTADV:X=BIN/__'USER1.DATASET.NAME1'

or

///USER1.DATASET.NAME1
//_USER1.DATASET.NAME1
/_/USER1.DATASET.NAME1
/__USER1.DATASET.NAME1
/FTADV:X=BIN/_/_USER1.DATASET.NAME1
/FTADV:X=BIN/_//USER1.DATASET.NAME1
/FTADV:X=BIN/__/USER1.DATASET.NAME1
/FTADV:X=BIN/___USER1.DATASET.NAME1

The choice of name type depends on the client. If consecutive slashes are not sent to the server, "/_" (or "/__" for a prefixed absolute dataset) is probably the best choice. The SFTP client interprets the file path to be absolute and does not add any directories in front of the name. If a file transfer advice string (see Advice String) is added in front of the file name, "__" (or "___" for a prefixed absolute dataset) is a safe choice. The dataset name becomes /FTADV:X=BIN/__DATASET.NAME1. The client interprets it as an absolute path to the file and does not change it. The SFTP server on the other hand recognizes the advice string /FTADV:X=BIN/ and interprets __DATASET.NAME1 to be the real name of the dataset //DATASET.NAME1.

z/OS has also library datasets, whose members are accessed using the dataset name //DATASET.NAME1(MEMBER1).

Again, parentheses may be special characters in some environments. The SFTP server introduces a new convention for accessing library members using a single slash as a member separator. The name becomes //DATASET.NAME1/MEMBER1.