Mirror log empty on primary but fine on the mirror
Well, its took months but i finally found the problem!

The sys.dm_os_performance_counters wasnt being populated at all on the primary server.

Turns out that the counters where not installed, i was able to do this manually as follows:

C:\Windows\system32&gt;lodctr "D:\Program Files\Microsoft SQL Server\MSSQL10_50.MSS
QLSERVER\MSSQL\Binn\perf-MSSQLSERVERsqlctr.ini"


Restarted SQL, and boom, the table is now being populated - including my mirroring statistics.