ERROR: could not open file "base/125542/12631" Corruption?

Hello, our postgresql 9.2.4 qa database (thankfully its just qa) seems to
be hosed.

Starting at around 3:39am last night I started seeing errors about missing
files and now I cannot run a pgdump or a vacuum without it complaining
about files that it cannot find with errors like this: ERROR: could not
open file "base/125542/12631". When I check the filesystem the files are
indeed not there. The 1am regular vacuum completed and its log is clean.
The postgres log is clean before these errors occurred.

Since this is qa we do not perform backups, and the solution if we cannot
repair the problem will be to create a fresh qa server but I am intrigued
about how to determine the source of the problem and the extent of the
problem.

Is there a way to force vacuum to continue on errors or an alternate way to
help determine all the missing files?

It might be totally unrelated, but yesterday morning on this qa server I
stopped postgres, and created a symlink to pg_xlog so that it was writing
to a different volume, and restarted. This was working fine all day so its
possibly a red herring but I thought I should mention it.

Any advice is appreciated, thanks!