When working with tape data sets, there are two alternative ways to specify the device unit on which the tape is to be mounted. Normally this can be done through the use of the site parameter unit, but in some situations it is not practical to do so. The environment variable SSH_SFTP_VOL_UNIT_MAP can be defined to provide a mapping between a volume serial number pattern and a device unit, allowing the unit to be deduced from the volume.

SSH_SFTP_VOL_UNIT_MAP may be set to a picture-clause type pattern matching a six character volume serial number, and followed by the unit to be used, in the form SSH_SFTP_VOL_UNIT_MAP=volume_pattern:unit_specification.

For example, SSH_SFTP_VOL_UNIT_MAP=AA9999:CART, where A is an alphabetic character and 9 is a decimal digit, means that volumes with a serial number consisting of two letters followed by four digits are to be allocated with UNIT=CART.

More specifically, SSH_SFTP_VOL_UNIT_MAP=TP00001:CART generates an allocation request for a tape with volume serial number TP0001 with unit CART.