The Control-M/Agent data collector (ctma_data_collector) gives the message: ERROR: No available disk space, 900M needed, exiting...

The Control-M/Agent does not need such a large default, so change the default for the Agent to 30 MB.

When executing the HCU data collector the default max-size is 300 MB.
The data collector requires 3 times this amount to be available on disk in order to run properly.
The default max_size is 300 MB for Control-M/Server and Control-M/Enterprise Manager and 300 MB for Control-M/Agent 9.0.18 and lower.  500MB for 9.0.19 and higher.

1) Explicitly set the parameter -max_size=<size in MB> when executing the data collector.
For example:  ctma_data_collector -max_size 20

2) Change the following line to a lower value (in MB) in the config.ini file:  max_size="####"
Unix:  <CTM Agent Home>/ctm/data/config.ini file to the lower value.
Windows:  <CTM Agent location>\data