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

[Steffen Maier]

On 8/26/21 8:47 AM, Martin Wilck wrote:
> 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.

+1

I think this depends on host and workload requirements and maybe other things. 
There might not be one simple answer.

FWIW, from a zfcp point of view: 
https://public.dhe.ibm.com/software/dw/linux390/lvc/zFCP_Best_Practices-BB-Webcast_201805.pdf#page=19
Distributed/parallel file systems with shared volumes might have their own 
requirement.
YMMV

We also have our opinion on dev_loss_tmo and fast_io_fail_tmo, but that's a 
different story 
[https://public.dhe.ibm.com/software/dw/linux390/lvc/zFCP_Best_Practices-BB-Webcast_201805.pdf#page=18].

-- 
Mit freundlichen Gruessen / Kind regards
Steffen Maier

Linux on IBM Z and LinuxONE

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