LVM: lvcreate fails: "Couldn't load device"

[Andrew Schulman <andrex@alumni.utexas.net>]

I'm trying to set up LVM for the first time.  I'm running
testing/unstable with kernel 2.6.7 and lvm2 version 2.00.24-1.  The 
dm-mod kernel module is loaded.  No udev or devfs here.

Since I've never done this before, I'm following the LVM HOWTO.  The 
following commands all succeed:

pvcreate /dev/hda1
vgcreate vg /dev/hda1
vgchange -ay vg

Now I want to create a logical volume, but the command seems to fail:

# lvcreate -L15000M vg
  device-mapper ioctl cmd 9 failed: Invalid argument
  Couldn't load device 'vg-lvol1'.
  Failed to activate new LV.

syslog says

Feb  4 15:04:17 helium kernel: device-mapper: : dm-linear: Device lookup 
failed
Feb  4 15:04:17 helium kernel: device-mapper: error adding target to 
table

Now, as I understand the HOWTO, lvcreate should have created the block 
device file /dev/vg/lvol1, that I can use to create filesystems on.  But 
it didn't.  OTOH, I do now have

# ls -l /dev/mapper
total 0
crw-------  1 root root  10, 63 Feb  3 16:31 control
brw-------  1 root root 254,  0 Feb  4 15:04 vg-lvol1

However all of lvdisplay, lvscan, vgdisplay, etc. act as though the 
volume has been created on /dev/vg/lvol1: e.g.

# lvscan
  ACTIVE            '/dev/vg/lvol1' [1.46 GB] inherit

(although the volume size is too small-- a separate problem I think).  
But there's no /dev/vg* in my filesystem.  Now maybe those devices 
aren't supposed to exist in /dev; maybe they're only logical devices 
that the kernel "sees".  I wouldn't be crazy about that, but I could 
live with it.  But then why the error about "Failed to activate new LV"?

LVM newbie is frustrated by this contradictory information and seemingly 
inexplicable behavior.  Any help appreciated.

Andrew.