----- Original Message ----- > I was trying to do some performance testing between using iSCSI on the > host as a diskfile to a guest vs the VM guest using the iSCSI device > directly. > > However, in the process of trying to establish a baseline performance > figure, I started increasing the MTU settings on the PCI-express NICs > with RTL8168B chips. > > First bottleneck was discovering the max MTU allowed on these is 7K > instead of 9K but googling seems to indicate that the RTL8168B is only > capable of 4K frames. > > I assumed 4K would still be better than nothing but unfortunately > bumping up the MTU to anything else but 1.5K caused the file transfers > (using NFS for easy testing), to hang at random points or more > accurate slow to a crawl. > > Checking the syslog, I discovered warnings that increasing MTU with > this adapter may cause problems. > > Searching around, it seems to be a common problem but there doesn't > appear to be any clear cut fix, including some suggestions to use a > third party driver. > > Does anybody know of a proven solution or is the Realtek chip itself > irrevocably broken/bugged that anything above the default 1500 will > simply not work? Realtek NICs are known to be some of the poorest interfaces available. A quality Intel or Broadcom NIC will set you back very little in terms of cost. Just replace it and be done. :) --Tim