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requested use case is having a Windows XP SP3 guest running in 64bit Ubuntu.
(Linux pcs 2.6.35-22-server #35-Ubuntu SMP Sat Oct 16 22:02:33 UTC 2010 x86_64 GNU/Linux)
I want this guest to access an LVM LV on the Ubuntu disk.

I've setup the following LVM config:
--- Logical volume ---

  LV Name                /dev/storage/sdc1  
  VG Name                storage  
  LV UUID                Zg5IMC-OlqB-prL5-fgg4-3A9A-OgKP-oZ0QkJ  
  LV Write Access        read/write  
  LV Status              available  
  # open                 0  
  LV Size                1.01 GiB  
  Current LE             259  
  Segments               1  
  Allocation             inherit  
  Read ahead sectors     auto  
  - currently set to     256  
  Block device           251:3  

--

1) I've setup a storage pool for /dev/storage
2) I've mkfs.vfat /dev/storage/sdc1
3) and made a virtual IDE disk in the virt-manager setup for the guest.
Target device: IDE Disk 2
Source path: /dev/storage/sdc1

--

Now when running XP (guest) Windows sees a new disk in Disk Manager and want's to install a partition on it, since it believes the drive is empty.
After formatting from within Windows I can put data on the new disk volume.

--
Back in Ubuntu however I cannot access this this any more since it created a partition within an LVM Logical Volume.

Running fdisk -l shows the following:

root@pcs:/media# fdisk -l /dev/storage/sdc1  

Disk /dev/storage/sdc1: 1086 MB, 1086324736 bytes  
32 heads, 63 sectors/track, 1052 cylinders  
Units = cylinders of 2016 * 512 = 1032192 bytes  
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes  
Disk identifier: 0x8d72e4f4  

             Device Boot      Start         End      Blocks   Id  System  
/dev/storage/sdc1p1               1        1050     1058368+   c  W95 FAT32 (LBA)  

--
which seems fine to me, but when trying to mount /dev/storage/sdc1p1 I get the following error:

mount /dev/storage/sdc1p1 /media/xp  
mount: special device /dev/storage/sdc1p1 does not exist  

which makes sense since in lvdisplay sdc1p1 does not exist

Main question:
I want to mount the vfat partition in both Ubuntu and XP
What am I missing here?????

regards, and thanks for your consideration.

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ps. same issue occurs on running a Ubuntu guest, lvm volumes seem to be at different abstraction levels for Virt-manager –  Nico de Smidt Mar 5 '11 at 17:29

1 Answer 1

up vote 0 down vote accepted

Ok, [SOLVED]

point is the device mapper does not create a mapping to the XP guest (or Ubuntu guest) partition which the guest created in the LV on Ubuntu host, automatically :-) (how should it now the guest did this ?)

in order to do fix this I found this other post: http://forums.gentoo.org/viewtopic.php?t=128781 and took the following items out of it to solve my issue.

1) do a sfdisk -d /dev/mapper/storage-sdc1 (the name of the LV in which XP created the partition
should print something like this:

partition table of /dev/mapper/storage-sdc1
unit: sectors  
/dev/mapper/storage-sdc1p1 : start=       63, size=  2116737, Id= c
/dev/mapper/storage-sdc1p2 : start=        0, size=        0, Id= 0
/dev/mapper/storage-sdc1p3 : start=        0, size=        0, Id= 0  
/dev/mapper/storage-sdc1p4 : start=        0, size=        0, Id= 0  

2) Create a mapping file for each partition, in my case this is just one line (I named it devmap.sdc1p1) Use start (last column) and size (second column)

cat devmap.sdc1p1 
#start      size    type    destination start
0 2116737 linear /dev/mapper/storage-sdc1 63

3) run dmsetup create sdc1p1 devmap.sdc1p1
this creates the ned DM device sdc1p1 (watch out, it creates it as sdc1 not storage-sdc1 as is convention)

4) mount the partition as mount -t vfat /dev/mapper/sdc1p1 /media/sdc1

5) :-) and some coffee

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