VAX 750/4.2 BSD disk trashing

[RSanders at usgs2-multics.arpa]

Relevant background:
  VAX 750, 4.2 BSD with few bug fixes, Emulex SC750 disk controller,
  Unit 0 - CDC 160 Mb winchester
  Unit 1 - Fujitsu 2351A Eagle
  Unit 2 - Fujitsu 2351A Eagle (newly installed)

Situation:
  Frustrated by a "severe burn-in" format on the #2 Eagle not finishing
after 11 hours, I stupidly try to mount the root partition that used to
be there, while in multi-user mode:

  mount /dev/hp2a /mnt

Bam - crash.  Can't boot off CDC drive anymore - several zillion files
and directories trashed, including /etc/init.  Luckily I keep a fresh
copy of the root partition on Eagle #1, but still, 4 hours of restoring
files from backup tapes during prime-time has given me a bad reputation.

Questions:

  Why didn't I get a simple "no filesystem present", or similar error
message, from mount or the kernel?

  Why did unit 0 get trashed?  Too many obscure files were trashed for
me to believe that the lack of a "sync" before crashing caused the
damage.

Flames of the form "You shouldn't have mounted that f.s.  without
running newfs first" are no longer useful.

-- Rex

p.s.  The "severe burn-in" format for the VAX 750/SC750/Eagle combo I
now estimate takes 13-14 hours - it's running now.  The "several hours"
listed in format(8) is severely understated.

-----
  You say kernal, I say kernel (or is it the other way around?)