[AusNOG] DCB in non-converged networks

[Robert Hudson]

I largely agree with Luke.  Given you're on a dedicated iSCSI network, keep
it simple.  DCB and other services will only add things that you'll later
need to troubleshoot and eliminate as the root cause of network issues on
your iSCSI network when they invariably happen (it's rare that I've come
across a well and consistently configured iSCSI network, and I've been
playing in that space since the mid 2000s).  Chances are your OS/hypervisor
vendor of choice publishes best practices for how to configure DCB - but as
noted, DCB is specifically there to deal with converged networks (where
your iSCSI traffic is sharing an ethernet fabric with other traffic types),
and you don't seem to have that situation.

Jumbo frames help in busy iSCSI networks by increasing throughput - but you
need to make sure every device from one end of the communications to the
other fully supports it.  Again, follow vendor advice here.  Getting this
wrong can cause all sorts of "fun".

Flow control, buffer tuning (large buffers tend to help with iSCSI
traffic), etc, can all help to eke out a few more small percentage points
of performance, but again, the further you drift from the KISS principle,
the more fun you're likely to have troubleshooting later.

Above all - set and document policy in all things, audit against that
policy both at initial setup and for drift during the lifecycle of the
environment.

On Thu, 9 Nov 2023 at 12:20, Luke Iggleden <luke at iggleden.com> wrote:

> Hi Andres,
>
> Unless you are running other services on the switch it's not useful.
>
> Typically these are the only useful changes:
>
> Jumbo Frames (YMMV), depends on vendor.
>
> Flow Control on (so hosts can issue back off - hopefully without dropping
> frames)
>
> Depending on the switch, buffer tuning.
>
> Don't use control plane things, like MLAG, Stacking, STP, etc etc. Flat
> fabric.
>
>
> Cheers,
>
> Luke Iggleden
>
>
> On 9/11/2023 11:14 am, Andres Miedzowicz wrote:
>
> Hello everyone,
>
>
>
> I wanted to get some opinions on the use of DCB and its associated
> protocols in a storage-only (iSCSI), non-converged network. Any thoughts
> about the pros and cons of enabling DCB in a scenario where 100% of the
> traffic on a switch is bi-directional iSCSI storage (virtual machines and
> backups)?
>
>
>
> Thanks in advance.
>
>
>
> Andres
>
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