[CentOS] Ethernet Quad

[John R Pierce]

  On 08/12/10 10:35 AM, Drew wrote:
> Not with the Intel Pro 1000's. The PCIe versions require a x4 slot in 
> the dual or quad configuration. Can't speak to the PCI-X version as I 
> don't have any in my inventory.


yeah, a single PCI-E 'lane' (eg, x1) is only about twice as fast as a 
PCI 32 bit 33Mhz desktop slot. (250MB/sec vs 133MB/sec burst).  As soon 
as you get into multiple devices contending for a channel, actual 
performance goes down considerably due to the overhead of contention 
negotiation.

PCI-E x4 has 4 of these lanes, so each of the 4 NICs can effectively 
have a lane to itself.   Full duplex gigE is, in theory, capable of 
120MB/sec read *and* 120MB/sec write at the same time, so this exceeds 
that single 32bit/33Mhz PCI slot by quite a lot..

PCI-E x4 is roughly equivalent to PCI-X (100-133Mhz, 64bit, about 
1Gbyte/sec), and any high performance IO device in a server should be in 
a x4 slot.