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[dm-devel] multipath.conf and polling_interval option seems misleading



After reviewing the code and doing some testing I have noticed that polling_interval did not work as expected. I had reviewed the description of the option for multipath.conf and it conflicted with the results that I had got
testing device-mapper-multipath on RHEL4/RHEL5.

$ cat /usr/share/doc/device-mapper-multipath-0.4.7/multipath.conf.annotated
#       # name    : polling_interval
#       # scope   : multipathd
#       # desc    : interval between two path checks in seconds
#       # default : 5
#       #
#       polling_interval 10

---------

The behaviour that I had expected based on the option's description above:
check path 1
wait polling_interval
check path 2
wait polling_interval
check path 1
wait polling_interval
check path 2
wait polling_interval

However after testing the results that I got was(with multipathd -v4):
example:
check path 1
check path 2
wait polling_interval
check path 1
check path 2
wait polling_interval

---------

The behaviour I seen in RHEL4 and RHEL5 was working as design after
reviewing the code and talking to a couple engineers.

The problem it seems is how I was reading the description of the option.
From my results in testing and talking with some engineers the "polling_interval" option actually means:

"The interval between checking all possible paths for all multipath paths"
----------

1) Is my assumption correct that "polling_interval" actually means:
"The interval between checking all possible paths for all multipath paths"

2) What is a better way to describe the "polling_interval" option?

3) Shouldn't we make it clearer for people who don't that that much experience with multipathing?

--sbradley


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