mounting ufs on ss10

hi all

I tried to mount a partition containing a ufs filesystem, generated under
solaris 7 on a ss10. With
   mount -t ufs -o ufstype=sun /dev/sdbx /mnt
I can mount the partition, and /etc/mtab reports: /dev/sdbx /mnt ufs
rw,ufstype=sun 0 0.

however, when I try to write something onto this partition, e.g. by writing
  mkdir /mnt/test
then the answer is: mkdir: cannot create directory '/mnt/test': Read-only
file system

so what's wrong? This problem happend with suse 7.3 and with 7.1 as well
and I remember to know this also from x86-linux when mounting vfat
filesystems (in this case, however, it appeared always after a certain time
of use and could be "fixed" by unmounting and remounting the
filesystem...). I remember that formerly, say 1.5 years ago, everything
worked with nearly the same hardware, the only difference being the first
hd, but not the second one, which should be mounted. So I suppose, it's a
thing of doing the commands correctly and not of sparc-linux itself. Any
suggestions?

Many thanks and a happy morning
Felix Hermann