Sample Facter plugin for sal that checks for disk I/O errors in the system.log and reports them.

diskerror.rb

require 'facter'

begin
  errors = 0
  File.open("/var/log/system.log").each_line do |line|
    begin
      if ( line.chomp =~ /disk.*: I\/O error/ )
        errors = 1
        break
      end
    rescue
    end
  end
end

Facter.add("diskerror") do
  setcode do
    errors
  end
end