[CentOS] iSCSI best practices

[Ross Walker]

On Dec 10, 2011, at 2:05 PM, "James A. Peltier" <jpeltier at sfu.ca> wrote:

> ----- Original Message -----
> | On Dec 10, 2011, at 1:49 PM, "James A. Peltier" <jpeltier at sfu.ca>
> | wrote:
> | 
> | > Jumbo frames is really the important thing when it comes to iSCSI.
> | > Having 9000 byte packets verses 1500 byte packets will dramatically
> | > increase your performance per interrupt. Most cheaper unmanaged
> | > switches cannot do this.
> | 
> | I want to break the myth here, jumbo frames are really only important
> | for 10Gbe+. On 1Gbe (or slow CPUs) they actually slow sequential
> | throughput due to the time to process each packet on 1Gbe and how that
> | in turn slows down packet interleaving and thus total throughput.
> | 
> | -Ross
> 
> On cheap network switches...  When you've got a switch that has 1 or more 10Gb uplinks and the rest of the switch is Gb, I doubt this is an issue, but I will agree that on *some* switches it may be detrimental to performance.

It's not a function of the switching fabric that changes things, but the speed of the ports.

If each packet takes 6 times longer to take off the wire then the system can handle 1/6th the number of simultaneous streams.

-Ross