[mdlug] OT: Gigabit Ethernet - Worth it?

[Dan Pritts]

On Wed, Dec 03, 2008 at 04:57:11PM -0500, Stan Green wrote:
> Oh ye experts of the network....
> 
> I do a lot of data transfer of large files (4gb - 40gb ) and large sets of 
> data (100gb+). These transfers take some time. I'm thinking of upgrading some 
> of the network to Gigabit Ethernet. I've read conflicting information about 
> Gigabit Ethernet; some say it is faster and some say the PC is the 
> bottleneck. My PC's tend to be a few (3-5) years old. I transfer data over 
> both NFS and Samba. Most of the large files go over Samba. If I replace the 
> NIC cards, cables and hub, should I expect to see a BIG difference in 
> transfer speed?

First, using a file-transfer protocol rather than Samba will almost
certainly give you some improvement.  SMB and NFS are chatty protocols
and have lots of pauses rather than full-time data transfer.

e.g., SFTP or plain old FTP, which doesn't do encryption so will
use less CPU.  make sure to firewall appropriately if you use plain
FTP.

Assuming this is all on a LAN, you will see some improvement by moving
to gigabit ethernet, no matter what you buy.

for the best performance, buy "server" ethernet cards, e.g., intel
pro/1000 SERVER adapter (there are also pro/1000 desktop adapters).
They really are better, but cost more too.

I'm not sure whether you get benefit from a $40 intel desktop
card vs. a $15 no-name card.  

as another poster mentioned, using jumbo frames will help too;
with 9000 byte frames you have 6x the data per packet.  The cheapest
gear will not support jumbo frames.  all switches, ethernet cards
and your upstream router must support jumbos to use them.  You can
get around the upstream router limitation by having a separate lan
or vlan for the data transfers.

a TCP offload feature on the ethernet card might help, or it might
make things worse.  I have seen cases where it hurt, and disabling
it made a difference.


danno
--
dan pritts
danno at umich.edu
734-929-9770