Re: A little more clarification -- Thank You!

[Ted Hilts <thilts@help-for-you.com>]

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Mark

Thankyou for your complete set of answers --  you scratched where you 
seemed to know I would be itchy. I have been over the manuals a number 
of times -- they are well written and I have no complaints.  But I 
seemed unable to completely "get it as intended".  You have bridged that 
problem for me.  Thanks to both you and Tim.  

I will try to download Tim's latest CD effort and test it but there is a 
good chance I will be unsuccessful in dowloading a very large file.

By way of introduction. One of the reasons why I wanted to be CERTAIN on 
these matters is because I would like to participate where I can on this 
list even though green around the ears with the whole subject of virtual 
machines.  Getting information over the internet is for me a major 
difficulty.  Today, I expect to install SuSE 9.1 (which I have working 
on another Linux machine) onto a Linux machine where I have 20 GIG  -- a 
full hard drive I can free up.  I may wait until I can make this a 200 
Gig drive.  Or I may go ahead and use the present 20 Gig drive for a 
learning exercise and then replace it. The idea is I want to create a 
specific area in my Lan for this Xen virtual technology.  Later, for 
this same machine,  I expect to replace another two 20 Gig drives for 
200 Gig drives for the same reason (my point #4 in previous email).  I 
have plans but no money for a network storage unit consisting of 8 200 
Gig drives if the cost of acquiring these drives drops. Also, I would 
like to get a 64 bit Linux machine and deploy it for the same reason. 
Certainly if I can manage this I will be able to provide a good test 
bed.  But first I have to develop some meaningful experience.  Too bad 
there is not a  "Xen For Dummnies" manual, that might do the trick.

I'm a retired IT person.  Before I retired I did a lot of code and 
database development.  Now, I do some code development but only to 
support various information processing that serves as content to web 
pages. I do my development work in my LAN (consisting of some 16 
machines), six Linux, 3 XP (ugh), and the remainder Win95. Two Linux 
machines do double duty as gateways to the Internet handling two Dial Up 
(about 28k max) (ugh) telephone lines and other work. I do perl 
development and other tasks on the Linux machines including uploading 
web pages to my USA based web server.   

There are no alternatives like Sattelite or DSL or cable services 
available as I live with my wife and my LAN and our dogs and cats in a 
rural area on a farm 60 miles NE of Edmonton, the capital city of the 
province of Alberta in Canada. My ISP has assured me this situation will 
not change. Dial Up for ever. There's gotta be an affordable way around 
this.  I cannot afford business rates for a corporate sattelite 
connection and the Bell "sattelite in -- ground line out" arrangement 
does not work well for ftp and it not supported for ftp. I had  hoped to 
use one of the Linux machines operating from my LAN out over sattelite 
to the Internet instead of the web server I operate in the USA.  I have 
about 2 Gig (used) on the USA web server. IF I ever get such a 
connection to my LAN  I will mirror all the information you people want 
to make available to the public and the list,

The 3 XP machines do double duty as data acquistion over the internet, 
shared storage, and web development. (the whole effort is non commercial 
non profit and religious) and are used as data servers to my main work 
activities.  The acquired data is used for web page content for my USA 
based web server. My bandwidth (even with 2 telephone lines) is 
inadequate for my needs.  So when I have the need to get technical 
information I have to divert one of the XP machines to that task so the 
data acquisition packages  can get that information for me.  When I'm 
not sure exactly what and where the needed information exists such as 
was the case with Xen I aim my data acquisition tools at a web site 
effectively mirroring it and it's references. But this takes a lot of 
time to happen (but frees me up for other pressing issues) because the 
other XP machines are also going 7x24 round the clock every day.  Then 
of course there is hoards of email and sometimes it takes half a day to 
get several hundred emails a day processed and get rid of the viruses 
and worms. Yes, I have a Windows Netscape based mail client (ugh) and am 
in the process of changing this to Linux. But I have to free up time 
before that can happen.

Enough of that.  If I want to surf the Internet and poke around reading 
web pages not yet downloaded then I have to suspend running processes 
that are often reluctant to suspend because the CPUs are going flat out. 
 I have been trying to get a service where I pay for specified 
downloaded information put onto a CD or DVD and then mailed to me. 
 Apparently there is someone that provides this service but this person 
has not responded to my email.  

Given that context, your complete set of answers is extremely helpful 
and I thank you and Tim again.

Thanks very much, Ted


Mark Williamson wrote:

>Hi Ted,
>
>  
>
>>Is what I have assumed correct, must there be an existing 2.4 or 2.6.x
>>kernel based Linux installation up and running which must be modified
>>(kernel modification or ported) to run Xen?
>>    
>>
>
>Yes.
>
>  
>
>>It is my understanding that 
>>the Xen source code installation or the binary installation both require
>>a properly pre installed fully functional Linux system as the basis of
>>Xen operation.  Once it's (pre installed linux distribution) 2.4.x or
>>2.6.x kernel has been modified to work with the Xen software and tools
>>we have created this Linux distribution into an Xen-based system called
>>Domain 0 that becomes so when shutdown and then booted???
>>    
>>
>
>Yes.
>
>  
>
>>#1 -- The BUILD:
>>The  Xen distribution includes 3 main components (Xen itself, ports of
>>Linux 2.4 and 2.6.x kernels to run on (with) Xen, and user-space tools
>>required to manage an Xen-based system) all of which assumes the
>>existence of an already installed and fully fuctional  pre existing
>>Linux system which must be adapted (to become the default Xen Linux
>>build identified as DOMAIN 0.
>>    
>>
>
>Correct.
>
>  
>
>>The Xen 
>>process (called xend) runs in highest privilege in DOMAIN 0 and  it's
>>code detects and starts secondary processors, sets up interrupt routing,
>>time slicing, and performs PCI bus enumeration as well as offloads
>>hardware support issues to DOMAIN 0 GUEST OS which is the modified pre
>>existing Linux installed distribution.
>>    
>>
>
>You're misunderstanding here - the lowlevel stuff (secondary processors, 
>interrupt routing, PCI, scheduling domains, etc, etc) happens in Xen.  Xen != 
>xend.
>
>Xen itself sits *below* the kernels of all the domains on the system 
>(including domain 0) and handles the low-level details of the system.  The 
>guest kernels are ported to run on top of Xen by using the interfaces it 
>provides.
>
>Xend is a management process that deals with the high-level management side of 
>the system.  It builds domains, records what domains are running, sends them 
>control messages, provides access to their consoles via TCP etc.  Xend isn't 
>required for the system to run, just to perform these management-plane 
>functions.
>
>  
>
>>As such, Xen provides a secure 
>>virtual machine for this GUEST OS, builds other domains using an OS
>>installed in a root file system placed on a partition and booted from
>>that partition, manages their virtual devices and performs
>>administrative tasks.
>>    
>>
>
>Root filesystems can be stored anywhere dom0 can access like a block device.  
>Files, LVM volumes, MD devices, whole disk drives, partiitons, network block 
>devices, etc. etc.
>
>  
>
>>My next question:
>>What exactly is an HTTP/S server -- apparently it is a requirement for
>>browser administration access to a Xen-based system? Is Apache such a
>>server and if not can it be turned into such a server???
>>    
>>
>
>HTTPS?  It's a secured version of HTTP.  I don't think you shouldn't need to 
>install anything extra to make this work - Twisted includes its own HTTP 
>server.
>
>(btw, Apache can serve over HTTPS but we don't use it in Xen)
>
>  
>
>>One more question:
>>Regarding the source code.  I have been reviewing Python and C
>>(gcc/gcc++) and was wondering if there was a high level diagram showing
>>dependencies (hierarchy based on caller and called)  and code utilized
>>(python, C, binary insertions, etc.)???
>>    
>>
>
>Nope, not really :-)  The Xen User Manual, Xend manual and Xen Interface 
>Manual (in the docs) directory might help you understand a bit more about the 
>system.  To comprehend the source code itself, I'm afraid there's not really 
>any kind of map.
>
>HTH,
>Mark
>
>  
>
>>Based on what I am learning here (mostly from you) I have been
>>constructing a very high level chart showing levels, key Xen processes,
>>and stuff like that.  I will send you a copy once I am sure the
>>information is correct and properly represents what is happening.
>>
>>Thank you very much in advance for your comments and advice.
>>
>>Ted
>>    
>>
>
>  
>


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