Tweak ncdu FAQ entry.

content/FAQ/_index.md

@@ -281,7 +281,28 @@ Access to HCC resources is separate from access to NU resources, so you do not l
 The Open OnDemand Apps are meant to be used for learning, development and light testing and have limited resources compared to the resources available for batch submissions. If the resources provided by OOD Apps are not enough, then they should migrate their workflow to batch script.
 
 #### How can I check which directories utilize the most storage on Swan?
-You can run `ncdu` from the Swan terminal with the file-system in question and (re)move directories and data if needed, e.g.,:
+You can run `ncdu` from the Swan terminal with the location in question and (re)move directories and data if needed, e.g.,:
 {{< highlight batch >}}
-ncdu $HOME
+ncdu $HOME/my-folder
 {{< /highlight >}}
+
+{{% notice info %}}
+If you have thousands or millions files in a location on Swan, please run `ncdu` only on a sub-directory you suspect may contain large numbers of files.
+{{% /notice %}}
+
+You may also use `ncdu` on locations in $WORK or $COMMON. Note that running `ncdu` puts additional load on the filesystem(s), so **please run it sparingly**.
+HCC suggests running `ncdu` once and saving the output to a file; `ncdu` will read from this file instead of potentially scanning the filesystem multiple times.
+To run `ncdu` in this manner, first scan the location using the `-o` option
+
+{{< highlight batch >}}
+ncdu -o ncdu_output.txt $HOME/my-folder
+{{< /highlight >}}
+
+Then use the `-f` option to start `ncdu` graphically using this file, i.e.
+
+{{< highlight batch >}}
+ncdu -f ncdu_output.txt
+{{< /highlight >}}
+
+Note that re-reading the filesystem to see changes in real time is not supported in this mode.  After making changes (deleting/moving files), a new output file
+will need to be created and read by repeating the steps above.