[dm-devel] [PATCH] multipath-tools: update no_path_retry value for IBM/2145

[Martin Wilck]

On Thu, 2021-08-26 at 00:24 +0200, Xose Vazquez Perez wrote:
> Based on current configs:
> https://www.ibm.com/docs/en/flashsystem-9x00/8.4.x?topic=system-settings-linux-hosts
> 
> Cc: Martin Wilck <mwilck at suse.com>
> Cc: Benjamin Marzinski <bmarzins at redhat.com>
> Cc: Christophe Varoqui <christophe.varoqui at opensvc.com>
> Cc: DM-DEVEL ML <dm-devel at redhat.com>
> Signed-off-by: Xose Vazquez Perez <xose.vazquez at gmail.com>
> ---
>  libmultipath/hwtable.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libmultipath/hwtable.c b/libmultipath/hwtable.c
> index 2a896440..58554cbb 100644
> --- a/libmultipath/hwtable.c
> +++ b/libmultipath/hwtable.c
> @@ -662,7 +662,7 @@ static struct hwentry default_hw[] = {
>                 /* Storwize family / SAN Volume Controller / Flex
> System V7000 / FlashSystem V840/V9000/9100 */
>                 .vendor        = "IBM",
>                 .product       = "^2145",
> -               .no_path_retry = NO_PATH_RETRY_QUEUE,
> +               .no_path_retry = 5,
>                 .pgpolicy      = GROUP_BY_PRIO,
>                 .pgfailback    = -FAILBACK_IMMEDIATE,
>                 .prio_name     = PRIO_ALUA,

Ref: https://github.com/opensvc/multipath-tools/issues/6

The question is on which basis IBM came up with this recommendation.
5 (aka 25s) is a rather low value. Some users may encounter unpleasant
surprises if we change the default this way, as it used to be infinite
before.

Using 5, the IBS 2145 would have the 2nd-lowest default in hwtable.c
after Dell PowerStore (3). Symmetrix has 6; all other arrays default to
10 or higher, many default to "queue".

Observing that the above is the documentation for the *Flashsystem*
9200,  I consider it likely that the value ".no_path_retry = 5" would
apply to flash-based IBM storage products, but not to the older
products such as the V7000, which unfortunately use the same device ID.

It'd be helpful if someone from IBM could jump in here...

Pondering the pros and cons, I vote for keeping the current defaults
for now.

Martin