About file and data set compression

Several tools or utilities are used to compress the files or data sets before they are sent to an FTP or SFTP server. The following table lists the compression tool or utility used for each file type and transfer method combination.

Table 1. Compression tool or utility used for each file type and transfer method
File Type	FTP and SFTP Transfer Methods	PDUU Transfer Method
System-supplied files	AMATERSE is used to compress the files.	PDUU is used to compress the files.
User-supplied data sets	AMATERSE is used to compress uncompressed data sets. If a data set has the low-level qualifier TRS, it is already compressed and will not be compressed again.	PDUU is used to compress the data sets. If a data set is already compressed, it will be compressed again.
User-supplied UNIX files	The pax command is used to compress uncompressed UNIX files. If a UNIX file has one of the following extensions, it is already compressed and will not be compressed again: gz, jar, pax, tar, z, or zip.	PDUU does not support UNIX files; therefore, z/OSMF always sends UNIX files using the FTP transfer method.