Had a similar problem not too long ago.  Run disklabel on /dev/sd2a, and
see what partitions are on the disk... should be like sd2a, sd2b, sd2g or
something... you want to mount not sd2a, but one of the others, like sd2g.
When you run fsck, run it on the same partition you'd mount (indicated by
disklabel... indirectly), so in my example you'd run fsck on sd2g.

  Here's a portion of disklabel's output in my case:
7 partitions:
#        size   offset    fstype   [fsize bsize   cpg]
  a:       32      144   unknown                        # (Cyl.    0*- 0*)
  b:        2   196606   unknown                        # (Cyl.   95*-
95*)
  c:   196608        0    unused        0     0         # (Cyl.    0 - 95)
  g:   196430      176    4.2BSD        0     0     0   # (Cyl.    0*-
95*)

  if you look thru these (ignoring the funky linewraps) you can see
/dev/sd1a thru sd1c are unknown or unused, only sd1g will mount or fsck
properly. =)

Hope this helps! =)

--MDP

Man invented alcohol, 
God invented grass.
Who do you trust?
-unknown

Clothes make the man.  Naked people have little or no impact on
society.
-Mark Twain