Re: Using multiple NICs

Robert Heller wrote:
"TH" <noaddress@xxxxxxxxxxxx>,
In a message on Tue, 2 May 2006 13:01:23 -0500, wrote :

"> I have this application that transfers huge amounts of data. The data source "> is an NFS share. What I would like to do is mount the NFS share so that the "> reads are from one NIC and move the data out through a different NIC.

It is doubtful that you can do *specificly* this.

"> "> Has anyone tried that before? What do you configure something like that?

What you really want to do is called 'bonding', where you bond two (or
more) NICs into a single logical NIC. Linux does support this. You
need to be sure your EtherNet switch supports it as well. Oh, it really
only makes sense if both machines (server AND client) are doing this.

You will get the same bandwidth effect as you want, since if you really
pull/push data at a rate high enough, the kernel will load share across
the two (or more) NICs, although you won't have any one NIC *dedicated*
to reads or writes (just like on a SMP system you won't have any one
processor dedicated to any specific processing).

Actually, given that modern Ethernet NICs and switches are generally full duplex devices, I would wager that bonding two NICs will offer better bandwidth than the OP's original proposal. After all, a 100 Mbit NIC (as an example, it applies equally to Gigabit NICs) can simultaneously read and write at 100 Mbit/sec (theoretically). With his proposal he would still have a 100 Mbit/sec read channel and a 100 Mbit write channel. With your suggestion for bonding two NICs he'd have 2 x 100 Mbit for reading and 2 x 100 Mbit for writing. I don't see that the dedicated-read-NIC and dedicated-write-NIC would offer any benefit whatsoever (assuming he's connecting both NICs to the same network).

A side note for the OP: if you're using Gigabit Ethernet, beware of the fact that a single GigE channel can theoretically consume almost all of the bandwidth on an ordinary 32-bit, 33MHz PCI bus. You'll need PCI-X or PCI Express (and/or multiple PCI busses) to get the benefit of multiple GigE NICs. You don't say what you're currently using so this may or may not be a consideration for you.
.

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