[CentOS] Multipath and iSCSI Targets

On Mar 20, 2010, at 4:52 PM, Drew <drew.kay at gmail.com> wrote:

>>> Depends on the target and the setup, ideally if you have 4 NICs you
>>> should be using at least two different VLANs, and since you have 4
>>> NICs (I assume for iSCSI only) you should use jumbo frames.
>>
>> Jumbo frames should only be used if your CPU can't keep up with the
>> load of 4 NICs otherwise it does add some latency to iSCSI.
>
> How much latency are we talking about?

That often depends on the NICs and switches, but in the realm of  
10-15% off throughput.

> I'm looking into gigabit networks at for both home & work and while
> home isn't so much an issue, work could be as I'm in the planning
> stages of setting up a gigabit network to allow some iSCSI NAS/SAN
> devices to back a bunch of VMware servers that we're due to get for
> our next refresh.

Set it up jumbo frame capable, but start out with standard frames and  
if you see the CPU getting pegged, try interrupt coalesence, if that  
isn't cutting it use jumbo frames.

-Ross