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Forum Discussion
For the networking experts: NAS VS Switch jumbo frames
I've been pondering on this for a while but have not found any definite answer:
Say you have a MTU of 9000 on your NAS, should your switch MTU be exactly 9000 as well or should it be over 9000 so the NAS and client are able to fit their packets inside that window...
This would boil down to what kind of max packet size negotiation is being done, how often it is being done and how long its taking ..
I believe a pretty standard max mtu size setting on switches is something like 9198.
p.s. I know the 'over 9000' meme, but I wasn't the one who came up with making 9000 the generic jumbo frame size :neener:
Say you have a MTU of 9000 on your NAS, should your switch MTU be exactly 9000 as well or should it be over 9000 so the NAS and client are able to fit their packets inside that window...
This would boil down to what kind of max packet size negotiation is being done, how often it is being done and how long its taking ..
I believe a pretty standard max mtu size setting on switches is something like 9198.
p.s. I know the 'over 9000' meme, but I wasn't the one who came up with making 9000 the generic jumbo frame size :neener:
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- Packet size negotiation varies by protocol, and some protocols have no method for doing it at all. Packets that are too large get fragmented (or dropped).
Sometimes these sizes include ethernet framing (18 bytes) and sometimes they don't. So that is something to keep in mind when you set them.
The best thing to do is to probe the maximum packet size with ping (using the -f and -l options with windows). - I actually managed to find an answer for this during the weekend on a site talking about (expensive) SAN setups ..
Switch MTU should be the transmitting clients MTU size + at least those 18 bytes.
The advice there was to put your SAN (/NAS) and clients on the same frame size (like, 9000) and then any networking gear in between at 9018 or higher.
Turns out I already had my setup configured like this (Pro pioneer + gigabit netgear switch of which I forgot the type) so no idea if it makes a lot of difference.
But I'm guessing a lot of people would make the 'mistake' of just setting everything to the same MTU size.
Again, this depends on whether the switch UI wants you to enter the maximum ethernet frame size (layer 2) or the layer-3 MTU. There are a lot of switches out there...Conz wrote: I actually managed to find an answer for this during the weekend on a site talking about (expensive) SAN setups ..
Switch MTU should be the transmitting clients MTU size + at least those 18 bytes.
The advice there was to put your SAN (/NAS) and clients on the same frame size (like, 9000) and then any networking gear in between at 9018 or higher.
Turns out I already had my setup configured like this (Pro pioneer + gigabit netgear switch of which I forgot the type) so no idea if it makes a lot of difference.
But I'm guessing a lot of people would make the 'mistake' of just setting everything to the same MTU size.
Verifying that the jumbo packets are getting through is easy to do. For a 9000 byte MTU (and Windows), open a cmd box and enter
ping -f -l 8972 xxx.xxx.xxx.xxx
where the xxx's are the IP address of the NAS.
If you see "Packet needs to be fragmented but DF set" then there is a problem with the configuration somewhere along the path.
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