From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx10.extmail.prod.ext.phx2.redhat.com [10.5.110.39]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v0HGRni3001865 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO) for ; Tue, 17 Jan 2017 11:27:49 -0500 Received: from mail.cropusainsurance.com (67-60-77-244.cpe.cableone.net [67.60.77.244]) by mx1.redhat.com (Postfix) with ESMTP id 9A80961E5B for ; Tue, 17 Jan 2017 16:27:46 +0000 (UTC) Date: Tue, 17 Jan 2017 08:27:40 -0800 (PST) From: Ken Goods Message-ID: <15337358.38.1484670456030.JavaMail.kgoods@Ken-PC> In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_37_20912667.1484670456028" Subject: Re: [linux-lvm] multipath_component_detection Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: To: Peter Rajnoha Cc: linux-lvm Mailing List ------=_Part_37_20912667.1484670456028 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Thanks so much Peter, exactly what I was looking for. Also thanks for the heads up on external_device_info_source, I'll use it. ----- Original Message ----- From: "Peter Rajnoha" To: kgoods@cropusainsurance.com Cc: "LVM general discussion and development" Sent: Tuesday, January 17, 2017 3:19:44 AM Subject: Re: [linux-lvm] multipath_component_detection On 01/16/2017 08:46 PM, Ken Goods wrote: > Hi all, > Just a quick question. I've been setting up a (iscsi) LUN and want to > create an LVM PV on it. > > The docs I have read are somewhat conflicted. Some say that the > underlying devices should be filtered, however according to comments in > lvm.conf it says that if multipath_component_detection is enabled, "LVM2 > will ignore devices used as component paths of device-mapper multipath > devices". > > So filtering is no longer necessary with LVM2? > The multipath component detection is an automatic filter in LVM2 (if enabled with devices/multipath_component_detection=1 in LVM configuration - that is used by default). So in this case you don't need to set up devices/global_filter (or devices/filter) manually. LVM will filter multipath components automatically by looking at the device stack and if it detects that there's a multipath device on top of certain set of devices, such devices are assumed as multipath components and they're filtered automatically. Of course, for this automatic filter to work correctly, you also need to have your multipath correctly configured - LVM doesn't know that the devices are multipath components unless there's multipath device already set up and running on top of those components. However, there's one improvement in this detection if you use devices/external_device_info_source="udev" in your LVM configuration (this is not used by default yet). In this case, LVM reads information from udev database which in turn has this information about multipath components directly from multipath and that one takes this information from its own configuration (the component WWID list in multipath's configuraton) - so in this case you don't even need to have multipath device set up yet on top of multipath components for LVM to detect multipath components properly. But usually, if your system is properly configured, you always have multipath device set up and running on top of multipath components. -- Peter ------=_Part_37_20912667.1484670456028 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable <= div style=3D'font-family: arial,helvetica,sans-serif; font-size: 10pt; colo= r: #000000'>Thanks so much Peter, exactly what I was looking for. Also than= ks for the heads up on external_device_info_source, I'll use it.

From: "Peter Rajnoha" <prajnoha@redhat.com&= gt;
To: kgoods@cropusainsurance.com
Cc: "LVM general di= scussion and development" <linux-lvm@redhat.com>
Sent: Tues= day, January 17, 2017 3:19:44 AM
Subject: Re: [linux-lvm] multipa= th_component_detection

On 01/16/2017 08:46 PM, Ken Goods wrote:
&= gt; Hi all,
> Just a quick question. I've been setting up a (iscsi) L= UN and want to
> create an LVM PV on it.
>
> The docs I = have read are somewhat conflicted. Some say that the
> underlying dev= ices should be filtered, however according to comments in
> lvm.conf = it says that if multipath_component_detection is enabled, "LVM2
> wil= l ignore devices used as component paths of device-mapper multipath
>= devices".
>
> So filtering is no longer necessary with LVM2?<= br>>

The multipath component detection is an automatic filter in= LVM2 (if
enabled with devices/multipath_component_detection=3D1 in LVM<= br>configuration - that is used by default). So in this case you don't need=
to set up devices/global_filter (or devices/filter) manually. LVM will<= br>filter multipath components automatically by looking at the device stack=
and if it detects that there's a multipath device on top of certain set=
of devices, such devices are assumed as multipath components and they'r= e
filtered automatically.

Of course, for this automatic filter to= work correctly, you also need to
have your multipath correctly configur= ed - LVM doesn't know that the
devices are multipath components unless t= here's multipath device already
set up and running on top of those compo= nents.

However, there's one improvement in this detection if you use=
devices/external_device_info_source=3D"udev" in your LVM configuration<= br>(this is not used by default yet). In this case, LVM reads informationfrom udev database which in turn has this information about multipath
= components directly from multipath and that one takes this information
f= rom its own configuration (the component WWID list in multipath's
config= uraton) - so in this case you don't even need to have multipath
device s= et up yet on top of multipath components for LVM to detect
multipath com= ponents properly.

But usually, if your system is properly configured= , you always have
multipath device set up and running on top of multipat= h components.

--
Peter

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