Optimising NFS for system files

Bernard Dugas bernard at dugas-family.org
Tue Dec 30 21:04:03 UTC 2008

Vince wrote:
>> Trying to change mtu, but don't look easy, where can i find the
>> possible range for ports ?

> MTU can be a pain, check what your switch supports, and the manpage for
> your network driver should say what MTU the nic supports.

Thank you for the method !

It seems that em and re are not behaving like they should :

re(4) says :
"The 8169, 8169S and 8110S also support jumbo frames, which can be 
configured via the interface MTU setting.  The MTU is limited to 7422, 
since the chip cannot transmit larger frames. "

But :
nfsserver# ifconfig re0 -mtu 7422
ifconfig: -mtu: bad value
nfsserver# ifconfig re0 -mtu 7421
ifconfig: -mtu: bad value

It should be a Realtek RTL 8111c but i don't know where to find the 
relationship to what pciconf -l gives me :
re0 at pci0:2:0:0: class=0x020000 card=0xe0001458 chip=0x816810ec rev=0x02 

em(4) says :
"The maximum MTU size for Jumbo Frames is 16114."

But :
client9# ifconfig em1 -mtu 8192
ifconfig: -mtu: bad value

with :
Dec 30 16:02:36 client9 kernel: em1: <Intel(R) PRO/1000 Network 
Connection 6.9.6> port 0x7f00-0x7f1f mem 0xfd4e0000-0xfd4fffff irq 17 at 
device 0.0 on pci7

client1# ifconfig em0 -mtu 8192
ifconfig: -mtu: bad value

with :
Dec 30 18:10:38 client1 kernel: em0: <Intel(R) PRO/1000 Network 
Connection 6.9.6> port 0xfe00-0xfe1f mem 0xf
dfc0000-0xfdfdffff,0xfdffe000-0xfdffefff irq 20 at device 25.0 on pci0

Now i understand better "MTU can be a pain" ;-)

Best regards,
Bernard DUGAS Mobile +33 615 333 770

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