From 3373221e4566a01fdbf5a71f4a58aa2d63b96605 Mon Sep 17 00:00:00 2001
From: Josh Samuelson <jsamuels@cse.unl.edu>
Date: Thu, 7 Mar 2019 16:06:04 -0600
Subject: [PATCH] Add a blurb about /common's compression capability and
reported space.
---
.../using_the_common_file_system.md | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/content/guides/handling_data/using_the_common_file_system.md b/content/guides/handling_data/using_the_common_file_system.md
index 3ca200bf..5a5ecdb0 100644
--- a/content/guides/handling_data/using_the_common_file_system.md
+++ b/content/guides/handling_data/using_the_common_file_system.md
@@ -65,4 +65,23 @@ to quickly do maintenance on a single cluster without having to unmount
for each cluster.
- If you use `module` things should be just fine!
+---
+### /common and used space reporting ###
+The /common file system has the capability to compress files so they store
+less data on the underlying disk storage. Tools like `du` will report the
+true amount of space consumed by files by default. If the files have been
+compressed before being stored to disk, the report will appear smaller
+than what may be expected. Passing the `--apparent-size` argument to
+`du` will cause the report to be the uncompressed size of consumed space.
+{{< highlight bash >}}
+$ pwd
+/common/demo/demo01
+$ python -c 'print "Hello World!\n" * 2**20,' > hello_world.txt
+$ ls -lh hello_world.txt
+-rw-r--r-- 1 demo01 demo 13M Mar 7 12:55 hello_world.txt
+$ du -sh hello_world.txt
+2.0K hello_world.txt
+$ du -sh --apparent-size hello_world.txt
+13M hello_world.txt
+{{< /highlight >}}
--
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