Auxiliary Storage Shortage
The SSH Tectia Server for IBM z/OS server program
sshd2 may make large demands on Auxiliary Storage.
If the server causes the total allocation of virtual storage in the system to approach the amount of Auxiliary Storage available, the system may enter an Auxiliary Storage Shortage state, which will require operator action to rectify. In this state the system will fail to start new processes.
When a client requests file statistics or file transfer the server may stage the file into memory. The server always stages MVS datasets and it stages HFS files if code conversion or line delimiter conversion is requested. Staging a dataset means that the server creates a Hiperspace memory file and copies the whole dataset into it. Each memory file will be the size of the converted dataset, up to 2 GB. A memory file is retained until a file transfer operation on it has ended or the connection is ended. The server may concurrently retain several memory files.
Clients that have a file-listing feature may request file statistics for every file in a directory. SSH Tectia Server for IBM z/OS supports file listing for HFS directories only, not for MVS files.
Thus a user on a remote machine may cause an Auxiliary Storage Shortage by executing the sftp command
ls in a directory that contains many files or several large files, or
get for a very large dataset or file. The user must be authenticated before entering commands.
A future release of SSH Tectia Server for IBM z/OS will allow the user to limit the total amount of virtual storage that is used on one client connection. Future releases of SSH Tectia Client, on several platforms, will remove the need for the server to stage files.
In the meantime, users should take precautions against the occurrence of an Auxiliary Storage Shortage situation by
- having a spare page dataset available
- being prepared to identify and cancel the process causing the shortage, and
- issuing the
PAGEADD command to make the spare page dataset available to the system.
Binary transfer of HFS files does not require staging and will not cause Auxiliary Storage Shortage.