From: shane bradley <sbradley@redhat.com>
To: device-mapper development <dm-devel@redhat.com>
Subject: Re: multipath.conf and polling_interval option seems misleading
Date: Thu, 29 Jan 2009 11:21:06 -0500 [thread overview]
Message-ID: <4981D772.9090704@redhat.com> (raw)
In-Reply-To: <4970B41C.1000509@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 3341 bytes --]
Patch attached for updated wording of documentation on polling_interval.
shane bradley wrote:
> Yeah the wording I think is the problem. Someone familiar with source
> code or multipathing will read that option differently.
>
> When someone reads the word path, they think of a single path to lun,
> then wait, check the next path to single lun.
> They are not thinking of all paths are checked at same time.
>
> After thinking about it, this would not be good behaviour because it
> could take forever (minutes) before a path is found dead.
> I think the problem is just the description of the option
> "polling_interval", it should be made clearer.
>
> --sbradley
>
> Chandra Seetharaman wrote:
>> On Fri, 2009-01-16 at 11:03 -0500, shane bradley wrote:
>>
>>> 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?
>>>
>>
>> IMO, the behavior seen is the proper behavior.
>>
>> If it does as per your interpretation, the seconds between checking of
>> the same path will depend on the number of paths to a storage, which may
>> not be acceptable.
>>
>> May be the wording in multipath.conf.annotated should be made clear.
>>
>>
>>> --sbradley
>>>
>>> --
>>> dm-devel mailing list
>>> dm-devel@redhat.com
>>> https://www.redhat.com/mailman/listinfo/dm-devel
>>>
>>
>> --
>> dm-devel mailing list
>> dm-devel@redhat.com
>> https://www.redhat.com/mailman/listinfo/dm-devel
>>
>
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
[-- Attachment #2: multipath.conf.annotated-polling_interval.patch --]
[-- Type: text/plain, Size: 440 bytes --]
--- multipath.conf.annotated.org 2009-01-29 11:03:22.000000000 -0500
+++ multipath.conf.annotated 2009-01-29 11:16:29.000000000 -0500
@@ -18,7 +18,8 @@
# #
# # name : polling_interval
# # scope : multipathd
-# # desc : interval between two path checks in seconds
+# # desc : the interval in seconds between polling all
+# devices that compose up all multipath devices
# # values : n > 0
# # default : 5
# #
[-- Attachment #3: Type: text/plain, Size: 0 bytes --]
next prev parent reply other threads:[~2009-01-29 16:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-16 16:03 multipath.conf and polling_interval option seems misleading shane bradley
2009-01-16 16:10 ` Chandra Seetharaman
2009-01-16 16:13 ` Bryn M. Reeves
2009-01-16 18:34 ` Chandra Seetharaman
2009-01-16 16:21 ` shane bradley
2009-01-29 16:21 ` shane bradley [this message]
2009-01-29 16:44 ` Bryn M. Reeves
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