Merge branch 'pr_641' into 'preview'

Document possibility to use alternative cache directories

Closes #641

See merge request !1151

doc.zih.tu-dresden.de/docs/data_lifecycle/permanent.md

@@ -31,6 +31,21 @@ submit jobs into the batch system. Running jobs are not affected.
      We have no feasible way to get the contribution of
      a single user to a project's disk usage.
 
+Some applications and frameworks are known to store cache or temporary data at places where quota
+applies. You can change the default places using environment variables. We suggest to put such data
+in `/tmp` or workspaces.
+We cannot list all applications that do this, but some known ones are
+
+| Application      | Environment variable              |
+|:-----------------|:----------------------------------|
+| Singularity      | `SINGULARITY_CACHEDIR`            |
+| pip              | `PIP_CACHE_DIR`                   |
+| Hugging Face      | `HF_HOME` and `TRANSFORMERS_CACHE`|
+| Torch Extensions | `TORCH_EXTENSIONS_DIR`            |
+
+Python virtual environments and conda directories can grow quickly,
+so they should also be placed inside workspaces.
+
 ## Global /projects Filesystem
 
 For project data, we have a global project directory, that allows better collaboration between the