delete partition from MO

[jumbler chi]

Hi All:
   Recently , I got  one HP Optical 2600Fx MO driver and 2.6G MO. 
I used /stand/sysinstall to create new partition and file system.
I saw one original partition of NTFS. 
I deleted entire partition , and create new. 
when I pressed 'W' to wrtte new partition information , I got a segment fault. 
Therefore , I executed 'newfs' directly , and it worked. 

then , the MO capacity is 2.6G. But the real mounted capacity is 1.2G. 

$ df -h /dev/da1a
Filesystem    Size   Used  Avail Capacity  Mounted on
/dev/da1a     1.2G   4.0K   1.1G     0%    /u01

What's wrong about to delete original partition and the capacity ? 


ps. My box is FreeBSD 5.2.1 R 
my dmesg information as following
..
acd0: CDROM <ATAPI-CD ROM-DRIVE-50MAX> at ata0-slave PIO4
Waiting 15 seconds for SCSI devices to settle
GEOM: create disk da0 dp=0xc6343050
GEOM: create disk da1 dp=0xc6344850
da1 at ahc0 bus 0 target 5 lun 0
da1: <HP C1113F 1.39> Removable Optical SCSI-2 device
da1: 5.000MB/s transfers (5.000MHz, offset 15), Tagged Queueing Enabled
da1: 1243MB (1273011 1024 byte sectors: 255H 63S/T 79C)