Doc: added space requirement to "Build Prerequisites"

Build prerequisites section does not include how much space Ceph
takes. A Ceph debug build can take 40 gigabytes by itself - double
the default size of many VMs by default, including CentOS 8 for
virt-manager. New contributors may be turned off or may not
understand why Ceph does not build. Also a warning on LVM taking
up too much disk space.

Signed-off-by: John B. Wyatt IV <jbwyatt4@gmail.com>

diff --git a/doc/install/build-ceph.rst b/doc/install/build-ceph.rst
index 147986e4c7d0c8127b6b634e40ecc9fefd108b59..5c93ca52d8b9bc82c10ce84b932d47dbafc2c257 100644 (file)
--- a/doc/install/build-ceph.rst
+++ b/doc/install/build-ceph.rst
@@ -3,16 +3,24 @@
 ============
 
 You can get Ceph software by retrieving Ceph source code and building it yourself.
-To build Ceph, you need to set up a development environment, compile Ceph, 
-and then either install in user space or build packages and install the packages. 
+To build Ceph, you need to set up a development environment, compile Ceph,
+and then either install in user space or build packages and install the packages.
 
 Build Prerequisites
 ===================
 
 
-.. tip:: Check this section to see if there are specific prerequisites for your 
+.. tip:: Check this section to see if there are specific prerequisites for your
    Linux/Unix distribution.
 
+A debug build of Ceph may take around 40 gigabytes. If you want to build Ceph in
+a virtual machine (VM) please make sure total disk space on the VM is at least
+60 gigabytes.
+
+Please also be aware that some distributions of Linux, like CentOS, use Linux
+Volume Manager (LVM) for the default installation. LVM may reserve a large
+portion of disk space of a typical sized virtual disk for the operating system.
+
 Before you can build Ceph source code, you need to install several libraries
 and tools::