16TiB ext4

[Curtis Doty]

I'm horsing around with ext4 again. This time on Fedora 10. Is there any 
sane reason why I cannot use the *full* 16TiB volume?

----8<----
# vgcreate foo /dev/mapper/mpath*
   Volume group "foo" successfully created
# lvcreate -L16T -nbar foo
   Logical volume "bar" created
# mkfs.ext4 -Tlargefile4 /dev/foo/bar
mke2fs 1.41.3 (12-Oct-2008)
mkfs.ext4: Size of device /dev/foo/bar too big to be expressed in 32 bits
         using a blocksize of 4096.
----8<----

But it appears to *really* allow up to one PE less than the full 16TiB, 
why?

----8<----
# vgdisplay foo
   --- Volume group ---
   VG Name               foo
   System ID
   Format                lvm2
   Metadata Areas        2
   Metadata Sequence No  2
   VG Access             read/write
   VG Status             resizable
   MAX LV                0
   Cur LV                1
   Open LV               0
   Max PV                0
   Cur PV                2
   Act PV                2
   VG Size               18.19 TB
   PE Size               4.00 MB
   Total PE              4769266
   Alloc PE / Size       4194304 / 16.00 TB
   Free  PE / Size       574962 / 2.19 TB
   VG UUID               tPk8uJ-gIYZ-GJSU-ssob-IoYu-8AUp-pHKALO
# lvremove -f foo/bar
   Logical volume "bar" successfully removed
# lvcreate -l4194303 -nbar foo
   Logical volume "bar" created
# mkfs.ext4 -Tlargefile4 /dev/foo/bar
mke2fs 1.41.3 (12-Oct-2008)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
1073741824 inodes, 4294966272 blocks
214748313 blocks (5.00%) reserved for the super user
First data block=0
131072 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
         32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
         4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968,
         102400000, 214990848, 512000000, 550731776, 644972544, 1934917632,
         2560000000, 3855122432

Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 35 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
----8<----

In my use case, I'm using much larger PEs, so the loss if just one is 
significant. Is this a bug in my thinking? Or in the userland tools?

../C