Off-topic, but I realised that you could search for two or more occurrences of a substring in a string with nested index() calls like this:

$str = 'N/A N/A blah blah blah SATA N/A blah blah N/A';

$substr = 'N/A';

if (index($str,$substr, index($str,$substr)+1 ) ) {
print "two or more occurrences of '$substr' in '$str'"
}
[download]

which is probably way faster than any RegEx method.