problems mounting swap on mfs

[Mipam]

Hi,

Im running FreeBSD 5.2.1-RELEASE-p1 and i'm having trouble mounting some
dirs on swap. pfstat -s yields:

Device          1K-blocks     Used    Avail Capacity
/dev/amrd0s1b     1599488        0  1599488     0%

When i put in /etc/fstab:

/dev/amrd0s1b  /try   mfs   rw,-s=65536   0   0

and then i try mount (yes i did create /try first)
i get:

mfs: bad device unit: amrd0s1b

Im using a raidconfig:

amr0: <LSILogic MegaRAID> mem 0xfcb00000-0xfcb3ffff,0xf0000000-0xf7ffffff
irq 18 at device 3.0 on pci4
amr0: <LSILogic PERC 4/Di> Firmware 4.10, BIOS B111, 128MB RAM

amrd0: <LSILogic MegaRAID logical drive> on amr0
amrd0: 34558MB (70774784 sectors) RAID 1 (optimal)
GEOM: create disk amrd0 dp=0xc4961b0c
ses0 at amr0 bus 0 target 6 lun 0
ses0: <PE/PV 1x3 SCSI BP 1.1> Fixed Processor SCSI-2 device
ses0: SAF-TE Compliant Device

What am i doing wrong?
Bye,

Mipam.