Disk naming are a little bit different between BSD and Linux. In addition ext2/ext3 file system are not so nicely support. However, you can mount your disk to read then.
List the disk available on the system
To get the list of connected disk to the system enter the following command:
camcontrol devlist
It will output something as follow:
<VBOX HARDDISK 1.0> at scbus0 target 0 lun 0 (ada0,pass0)
<VBOX CD-ROM 1.0> at scbus1 target 0 lun 0 (pass1,cd0)
To get the partitions available:
ls /dev/ada0*
Mounting the filesystem
mount -t ext2fs /dev/ad0s1 /mnt/linux