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. 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.
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.
SSH Tectia Server for IBM z/OS allows limiting the total amount of virtual storage that is used on
one client connection. The limit can be set in the SSH_SFTP_STAGEFS_CACHE_SIZE_LIMIT
environment variable.
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.
