Text 16683, 130 rader
Skriven 2006-03-21 07:40:04 av Jeff Guerdat (1:229/2000)
  Kommentar till text 16656 av MARTIN ATKINS (1:123/140)
Ärende: need time?
==================
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.

VNC is simply a viewer into another computer's OS - think of using X windows
across the network.  VMware (and similar) actually run the OS as a process
under your own computer's OS (Linux on Windows, Windows on Linux, Linux on
Linux and Windows on Windows).  Only one OS at a time, given today's hadware
and software, can control the hardware.  A virtual machine *THINKS* it's
controlling something but underlying software is just telling the OS what it
wants to hear.  Hence, a VM cannot control the local hard disks since it thinks
it's running on something else.  In order to access local facilities, the
underlying software must make it available or you must pretend you're on two
separate machines.  In our case, access to the local hard drive had to be
obtained via networking (one computer, separate and unto itself, must use
networking to access another computer's resource).

 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.

The RAID issue just clouds the picture (a RAID drive is seen as one large drive
and certainly has the same sort of mount points as a single drive).  There is
no remote machine since the XP VM is running on a Linux laptop.  For the
record, I can't run anything newer than Redhat 9 on the desktop machine since
there's no RAID driver for the newer kernels.  That's a story by itself and has
no bearing here.  The hardware at issue is ANY hardware on the machine where
the VM runs on top of the host OS (XP is running in a VM on top of Linux in
this instance).  The XP VM cannot see the hard drive, network card or even the
keyboard - they're all emulated in one way or another.  Again, think of two
separate machines with one trying to use the other's resources. Since the only
disk the VM sees is it's own emulated disk (it's a large file that's made to
look like a physical disk by the underlying driver of the virtual machine) it
has no physical access to the real hard drive.  The VM can, however, talk to
the host OS as if it were another computer on the network and mount drives that
way.  This is the method my son has to take to access files stored on the drive
by the host OS. (BTW, "host OS" refers to the one that runs when you boot the
computer.  The "guest OS" is the one that runs in the virtual machine.)

 JG>> So, repartitioning was  no
 JG>> needed since the VM would never be able to use it anyways. 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?

major minor  #blocks  name

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

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

 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.

Yep, Fedora Core 4.  No way I'd use a GUI backup tool - dump and restore work
fine.  However, backing up to a remote device is problematic since wireless
under Linux is, shall we say, problematic.  I have to use ndiswrapper to allow
me to use the Windows driver for my Cardbus NIC and, of course, that would be a
problem when trying to restore from a rescue CD boot.  I suppose I could swap
in the Ethernet card but I don't care enough to do so.  If I really wanted to
(I don't) I'd just save the home directories and blow it all away to start
over.  There's no advantage right now to do so.

 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.

Nope, you just are having a hard time grasping the idea of virtual machines,
etc.  If I needed to rebuild, I'd just be doing a Fedora install followed by
copying some files.  The virtual machine is self-contained in some (VERY) large
files that can be easily copied all over the place.  Which is how I got it
"installed" on the Linux laptop in the first place.

 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
....
 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.

Thanks for the offer but I've been building Unix (Solaris) machines for 15
years and am well-versed in partitioning and why things (don't) make sense. 
Linux is new to me so the install was done with defaults.  Now that I can see
what Redhat did, I can make intelligent decisions as to how to proceed in the
future.  The current partition scheme only has a problem if I need to shrink
partitions. I'm no longer interested in that since there's no need.  Next time
I rebuild in, say, 2 years, I may repartition differently.  Or not.  ;)

-- 
Jeff Guerdat

Then you wake up at the high school level and find out that the
illiteracy level of our children are appalling.
                                                 Dubya

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