--- wikisrc/ports/xen/howto.mdwn	2014/12/24 15:31:36	1.32
+++ wikisrc/ports/xen/howto.mdwn	2014/12/24 15:54:50	1.33
@@ -285,20 +285,33 @@ installed 4.1 or 4.2):
         xend=YES
         xenbackendd=YES
 
-For 4.1 (and thus xm), add to rc.conf:
+For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
 
         xend=YES
         xencommons=YES
 
 TODO: Explain why if xm is preferred on 4.1, rc.d/xendomains has xl.
+Or fix the package.
 
-For 4.2 with xl, add to rc.conf:
+For 4.2 with xm, add to rc.conf
+
+        xend=YES
+        xencommons=YES
+
+For 4.2 with xl (preferred), add to rc.conf:
 
         TODO: explain if there is a xend replacement
         xencommons=YES
 
 TODO: Recommend for/against xen-watchdog.
 
+After you have configured the daemons and rebooted, run the following
+to inspect Xen's boot messages, available resources, and running
+domains:
+        xm dmesg
+	xm info
+	xm list
+
 Updating NetBSD in a dom0
 -------------------------
 
@@ -332,19 +345,51 @@ Unprivileged domains (domU)
 ===========================
 
 This section describes general concepts about domUs.  It does not
-address specific domU operating systems or how to install them.
-
-Provided Resources for PV domains
----------------------------------
-
-TODO: Explain that domUs get cpu, memory, disk and network.
-Explain that randomness can be an issue.
+address specific domU operating systems or how to install them.  The
+config files for domUs are typically in /usr/pkg/etc/xen, and are
+typically named so that the file anme, domU name and the domU's host
+name match.
+
+The domU is provided with cpu and memory by Xen, configured by the
+dom0.  The domU is provided with disk and network by the dom0,
+mediated by Xen, and configured in the dom0.
+
+Entropy in domUs can be an issue; physical disks and network are on
+the dom0.  NetBSD's /dev/random system works, but is often challenged.
+
+CPU and memory
+--------------
+
+A domain is provided with some number of vcpus, less than the
+number of cpus seen by the hypervisor.  For a dom0, this is controlled
+by the boot argument "dom0_max_vcpus=1".  For a domU, it is controlled
+from the config file.
+
+A domain is provided with memory, In the straightforward case, the sum
+of the the memory allocated to the dom0 and all domUs must be less
+than the available memory.
+
+Xen also provides a "balloon" driver, which can be used to let domains
+use more memory temporarily.  TODO: Explain better, and explain how
+well it works with NetBSD.
 
 Virtual disks
 -------------
 
-TODO: Explain how to set up files for vnd and that one should write all zeros to preallocate.
-TODO: Explain in what NetBSD versions sparse vnd files do and don't work.
+With the file/vnd style, typically one creates a directory,
+e.g. /u0/xen, on a disk large enough to hold virtual disks for all
+domUs.  Then, for each domU disk, one writes zeros to a file that then
+serves to hold the virtual disk's bits; a suggested name is foo-xbd0
+for the first virtual disk for the domU called foo.  Writing zeros to
+the file serves two purposes.  One is that preallocating the contents
+improves performance.  The other is that vnd on sparse files has
+failed to work.  TODO: give working/notworking NetBSD versions for
+sparse vnd.  Note that the use of file/vnd for Xen is not really
+different than creating a file-backed virtual disk for some other
+purpose, except that xentools handles the vnconfig commands.
+
+With the lvm style, one creates logical devices.  They are then used
+similarly to vnds.
 
 Virtual Networking
 ------------------
@@ -362,6 +407,18 @@ dom0.  This is often appropriate when ru
 One can construct arbitrary other configurations, but there is no
 script support.
 
+Sizing domains
+--------------
+
+Modern x86 hardware has vast amounts of resources.  However, many
+virtual servers can function just fine on far less.  A system with
+256M of RAM and a 4G disk can be a reasonable choice.  Note that it is
+far easier to adjust virtual resources than physical ones.  For
+memory, it's just a config file edit and a reboot.  For disk, one can
+create a new file and vnconfig it (or lvm), and then dump/restore,
+just like updating physical disks, but without having to be there and
+without those pesky connectors.
+
 Config files
 ------------
 
@@ -526,7 +583,7 @@ working vif-bridge is also provided with
 
     #!/bin/sh
     #============================================================================
-    # $NetBSD: howto.mdwn,v 1.31 2014/12/24 15:30:45 gdt Exp $
+    # $NetBSD: howto.mdwn,v 1.32 2014/12/24 15:31:36 gdt Exp $
     #
     # /usr/pkg/etc/xen/vif-bridge
     #