----- 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
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