Text 16686, 273 rader
Skriven 2006-03-23 00:52:00 av MARTIN ATKINS (1:123/140)
     Kommentar till en text av JEFF GUERDAT
Ärende: need time?
==================
-=> JEFF GUERDAT wrote to MARTIN ATKINS <=-

 JG> MARTIN ATKINS -> JEFF GUERDAT wrote:
 JG>> However, it didn't stick with me that a VM has no contact
 JG>> with the local hardware and that it couldn't see, much less mount, a
 JG>> local partition.

 MA> Hmm. I've used VNC and perhaps it's not the same but if you where
 MA> running Linux on the fully partitioned machine you couldn't
 MA> umount the disk because the client would need it. I think however
 MA> you are probably talking about the RAID devices so i can't help
 MA> you there.

 JG> VNC is simply a viewer into another computer's OS - think of using X
 JG> windows across the network.  
 
X windows is not XP. Why confuse the issue? You are talking about a
VNC across a network. A VNC connection should act as if you are on 
board depending on your permissions.  
 
JG> VMware (and similar) actually run the OS
JG> as a process under your own computer's OS (Linux on Windows, Windows on
JG> Linux, Linux on Linux and Windows on Windows). Only one OS at a time,

Yes!! So if Win can't see Linux partitions it won't see them in a
VMC session. A VNC session using Linux to Linux will but by using 
RAID devices you are adding another layer of complexity.

JG> given today's hadware and software, can control the hardware.  A
JG> virtual machine *THINKS* it's controlling something but underlying
JG> software is just telling the OS what it wants to hear.  

I don't know about VMware but in princible a Linux VNC connection 
importing a screen session from a Win machine should be able to
to use the hardware on the remote as if you were at the keyboard or 
the mouse.  

JG> Hence, a VM cannot control the local hard disks since it thinks 
JG> it's running on something else.  

Why would you use VMware on your local machine to comunicate 
with it's self? You call in another consul to deal with local
conditions. A Win to Linux session won't work on Linux partitions
"period". A Linux to remote Linux will do every thing possible
to stop you for security reasons. It can be done but that is
a matter of permission. 

JG> In order to access local facilities, the underlying
JG> software must make it available or you must pretend you're on two
JG> separate machines.  

I get the feeling you are trying to overcome a hardware problem on 
your local machine. ;) If this is so then IMHO you are going about
it all wrong. You can't boot two opperating systems on one machine
at the same time. At least not yet. ;)

Linux is the server and under many circumstances these days a 
desktop. If you need to send data to an other system then use
an eth0 or what ever. Use the tools such as FTP server or Telnet
server etc to allow the client to call you. Then the client (Win)
can deal with it. If that is not an option then mount the Win
partition and copy the data to it and reboot to the Win operating
system. 

JG> In our case, access to the local hard drive had to
JG> be obtained via networking (one computer, separate and unto itself,
JG> must use networking to access another computer's resource).

Then you would be looking at something like "rlogin" or "ssh".
You can't play with the remotes partitions because it needs 
them to be the client or the host. ;) You could play with non core 
partitions but again the remote would scream about permissions. 
Do you really want a remote system having control over what may 
be an important server?

JG>> The "disk" the VM sees is just a large file in the
JG>> host operating system, not the hardware.

MA> By hardware you mean RAID? Im not sure if the remote box is using
MA> XP. I presume RAID devices don't have mount points.

JG> The RAID issue just clouds the picture (a RAID drive is seen as one
JG> large drive and certainly has the same sort of mount points as a single
JG> drive).  

Ok lets leave RAID out of this because it seems to be incidental.

JG> There is no remote machine since the XP VM is running on a
JG> Linux laptop.  

Big mistake. How do you reconcile interrupt calls much less BIOS
clashes?

JG> For the record, I can't run anything newer than Redhat 9
JG> on the desktop machine since there's no RAID driver for the newer
JG> kernels.  

Then don't use RAID. ;) Why can't you just have a conventional
setup?

JG> That's a story by itself and has no bearing here.  The
JG> hardware at issue is ANY hardware on the machine where the VM runs on
JG> top of the host OS (XP is running in a VM on top of Linux in this
JG> instance).  The XP VM cannot see the hard drive, network card or even
JG> the keyboard - they're all emulated in one way or another.  

Yes. If you are running Linux and importing a screen session from
another machine then Linux handles the BIOS and interrupts on the
local machine. The VNC client is controlled by the WIN operating 
system as are the interrupts and BIOS calls on the remote machine.
 
LG> Again,
JG> think of two separate machines with one trying to use the other's
JG> resources.

Ok now you think of one machine being used by two operating systems
trying to use it's interrupts and BIOS. It ain't gonna happen any time
soon. ;)

JG> Since the only disk the VM sees is it's own emulated disk
JG> (it's a large file that's made to look like a physical disk by the
JG> underlying driver of the virtual machine) it has no physical access to
JG> the real hard drive.  

It doesn't matter. You cannot run two operating systems on one
machine at the same time. You can import screen output from another
system and control the mouse and have keyboard input but it is not
running on the local system. You are only controlling buffer in
and out on the remote system. 

JG> The VM can, however, talk to the host OS as if it
JG> were another computer on the network and mount drives that way.  

Yup.

JG> This
JG> is the method my son has to take to access files stored on the drive by
JG> the host OS. (BTW, "host OS" refers to the one that runs when you boot
JG> the computer.  The "guest OS" is the one that runs in the virtual
JG> machine.)

Yes the host is the one the boots the system or it can be the client
on a network.

The "client" is the _remote_ (guest) on your local machine.

You cannot boot Linux and XP on one machine at the same time
without a serious train crash.

JG>> So, repartitioning was  not
JG>> needed since the VM would never be able to use it anyways. 

Yes it can. If you have dual boot then a VM server on the local system 
can communicate with a remote VM client regardless of the opperating
systems. 

JG> However, I'd
JG>> still like to figure out if it's possible to shrink that "extended"
JG>> partition and the logical drives inside it.

 MA> Just to help me under stand whats going on could you
 MA> cat /proc/partitions for me?

 JG> major minor  #blocks  name

 JG>    3     0   39070080 hda
 JG>    3     1     104391 hda1
 JG>    3     2   38965657 hda2
 JG>  253     0   37879808 dm-0
 JG>  253     1    1048576 dm-1

 JG> The disk is fully allocated and used for Linux.  The emulated disk is
 JG> an 8GB file in the Linux filesystem.

My math may be wrong but that looks like a 40 Gig drive. The first
partition is a hundred Meg which leaves 39.9 gig. The second partition 
is over 39 Gig, dm-0 is about 38 Gig, dm-1 is about 1 Gig.

JG>> It appears to not be
JG>> possible at the moment  but tools will probably continue to evolve over
JG>> time. One thing that may have been easier would be to shrink the ~100MB
JG>> /boot partition by 25-50MB (who needs THAT many kernels installed?) and
JG>> stick the FAT partition in there.  Still, without a dual boot machine,
JG>> it makes no difference/sense.

MA> Am i right you are using Fidora? Are going to be happy with this machine
MA> the way it is? You should have a GUI backup facilty some where. IMHO
MA> you should back up and dump the back up on a remote. Then start again.

JG> Yep, Fedora Core 4.  No way I'd use a GUI backup tool - dump and
JG> restore work fine.  

Yes i know but this is _your_ server and any tool to build it and
to maintain stability is fair game.

JG> However, backing up to a remote device is
JG> problematic since wireless under Linux is, shall we say, problematic.

You can't keep throwing up new complexities at me. If wireless is a 
problem then you deal with it from a stable environment.

JG> I have to use ndiswrapper to allow me to use the Windows driver for my
JG> Cardbus NIC and, of course, that would be a problem when trying to
JG> restore from a rescue CD boot.  I suppose I could swap in the Ethernet
JG> card but I don't care enough to do so.  If I really wanted to (I don't)
JG> I'd just save the home directories and blow it all away to start over.
JG> There's no advantage right now to do so.

I can see that. But you may need to upgrade systems one day. If not
we would all be using 286s. There is a big advantage to be had by 
thinking ahead even if for the time being it is not a necessity. 

MA> There is a lot to learn with Linux and mistakes happen. If you carry
MA> on with this setup it's going to be harder and harder to rebuild.

JG> Nope, you just are having a hard time grasping the idea of virtual
JG> machines, etc.  

I understand VNCs. :) It was one of the first things i looked at 
because like most people i prefer to deal with what i am most familiar 
with. I got hooked on the more intricate side of networking and gradualy
i moved away from thinking DOS/Win interface and so although i can see
the merit of using a comforatable interface i can happily work outside
those narrow peramiters.

JG> If I needed to rebuild, I'd just be doing a Fedora
JG> install followed by copying some files.  The virtual machine is
JG> self-contained in some (VERY) large files that can be easily copied all
JG> over the place.  Which is how I got it "installed" on the Linux laptop
JG> in the first place.

Laptops may be problamitic because of the limitations of the hardware
but most half decent laptop owners would probably have a desktop
at home that they can plug into. ;)

JG>> Needless to say, I won't be using default partitions any more.  I'll
JG>> use separate primary partitions unless I have a specific reason to do
JG>> otherwise.

MA> I know it's a tough lesson to learn. :( You don't need a "/boot" because
MA> it is included in "/" and so is "/root", "/etc", "/usr", as are all
MA> the core directories needed for booting. On my bloated system the
JG> ....
MA> If you tell me how much disk Linux can have i will give you
MA> a reasonable partitioning regime for it. I am not an expert and
MA> at a later date you may decide you have a better way. However
MA> i have learned through hours of trial an error to come up with
MA> a reasonable way of doing things. I can almost guarantee you will not
MA> be happy with the way things are now. If you want to talk to me
MA> privately i will give you my email address and explain exactly why
MA> i do it the way i do.

JG> Thanks for the offer but I've been building Unix (Solaris) machines for
JG> 15 years and am well-versed in partitioning and why things (don't) make
JG> sense. 

I didn't have you peged as a fool. ;)

JG> Linux is new to me so the install was done with defaults.  Now
JG> that I can see what Redhat did, I can make intelligent decisions as to
JG> how to proceed in the future.  The current partition scheme only has a
JG> problem if I need to shrink partitions. I'm no longer interested in
JG> that since there's no need.  Next time I rebuild in, say, 2 years, I
JG> may repartition differently.  Or not.  ;)

For the time being you can't run two operating systems on one machine.
You are either running a server on your system or client. You can't 
have both. That doesn't mean you can't provide say HTTP service to
your local system it just means you can't effectively run Linux and
Win at the same time. 

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