[dm-devel] [PATCH] libmultipath: update INFINIDAT builtin config

[Xose Vazquez Perez]

On 08/28/2017 03:59 PM, Arnon Yaari wrote:

>> On 25 Aug 2017, at 3:26, Xose Vazquez Perez <xose.vazquez at gmail.com> wrote:

>> On 08/22/2017 03:37 PM, Arnon Yaari wrote:

>>> -		.pgfailback    = -FAILBACK_IMMEDIATE,
>>> +		.pgfailback    = 30,

>> Why is it needed?

> All the values suggested here are the values that the company’s interoperability
> team found work best for the product on Linux. The timeout values are there
> because in some upgrade scenarios we don’t want to fail devices until the
> upgrade finishes.

Were they tested with a *current* kernel and multipath-tools?

> I don’t think there is a reason to add in-line comments in the code to
> explain the values (none of the other vendors are doing that).

It should be documented in the body of the git patch(changelog).

Anything other than default values must be documented.
This is a standard request: https://marc.info/?t=149850399700003

>>> +		.selector      = "round-robin 0",
>>
>> round-robin is the dumbest, queue-length is smarter and
>> service-time is the smartest and default selector.
> 
> Regardless of which algorithm is “dumbest” or “smartest”, round-robin
> is a legitimate path selection algorithm that the vendor decided works
> best with its product. The vendor knows its product best :)
> The product’s customers set the values suggested here (manually or
> using tools provided by the vendor), whether they are upstream or not.

In an *ideal environment* , "round-robin" "queue-length" and "service-time"
work the same way, doing a round robin distribution.

But when things get ugly, "round-robin" could lost data.

"service-time" works much better in any environment, even asymmetrical.
In highly congested links, with different link speeds, faulty paths, ...

path_selector is like TCP congestion control algorithm.

>>> +		.no_path_retry = NO_PATH_RETRY_FAIL,
>>
>> Default value.
> 
> Isn’t the default NO_PATH_RETRY_UNDEF?


Practically it's the same: https://marc.info/?l=dm-devel&m=147854542623733


Thank you.