Re: multipathd removing DM devices that don't belong to it

Re: multipathd removing DM devices that don't belong to it

[Artem Danielov]

[-- Attachment #1.1: Type: text/plain, Size: 884 bytes --]

Hi,
Any chance you guys have looked into this problem? Thank you!

From: Artem Danielov
Sent: Tuesday, June 16, 2015 15:02
To: 'dm-devel@redhat.com'
Subject: multipathd removing DM devices that don't belong to it

Hello,
Looking for an advice on whether this is an expected behavior or a bug.
device-mapper-multipath-0.4.9-77.el7.x86_64

When multipathd service starts it will remove any DM devices with multipath target, even if the underlying devices are blacklisted.
We are trying to use dmsetup directly  to implement custom multipath management logic separate from multipathd. But unfortunately if multipathd is present and enabled it removes DM devices with multipath target that we create.

Is this a bug?

Thanks for your help!

Artem Danielov | Chief Technology Officer | FlashGrid Inc. | artem@flashgrid.io<mailto:artem@flashgrid.io> | +1-503-568-5249


[-- Attachment #1.2: Type: text/html, Size: 3555 bytes --]

[-- Attachment #2: Type: text/plain, Size: 0 bytes --]

Re: multipathd removing DM devices that don't belong to it

[Hannes Reinecke]

On 07/24/2015 07:53 PM, Artem Danielov wrote:
> Hi,
> 
> Any chance you guys have looked into this problem? Thank you!
> 
>  
> 
> *From:* Artem Danielov
> *Sent:* Tuesday, June 16, 2015 15:02
> *To:* 'dm-devel@redhat.com'
> *Subject:* multipathd removing DM devices that don't belong to it
> 
>  
> 
> Hello,
> 
> Looking for an advice on whether this is an expected behavior or a bug.
> 
> device-mapper-multipath-0.4.9-77.el7.x86_64
> 
>  
> 
> When multipathd service starts it will remove any DM devices with
> multipath target, _even if the underlying devices are blacklisted_.
> 
> We are trying to use dmsetup directly  to implement custom multipath
> management logic separate from multipathd. But unfortunately if
> multipathd is present and enabled it removes DM devices with
> multipath target that we create.
> 
Well, hardly surprising.
ATM multipathd expects to be the only one creating multipath tables,
so of course it would try to 'rectify' the situation.

What one could try is to use a different UUID prefix (ie something
else than 'mpath') and then teach multipath to ignore all
device-mapper devices of type 'multipath' but without the 'mpath'
UUID prefix.

>  
> 
> Is this a bug?
> 
Not as such.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

Re: multipathd removing DM devices that don't belong to it

[Artem Danielov]

[-- Attachment #1.1: Type: text/plain, Size: 2797 bytes --]

Hi Ben,
Unfortunately, I missed your response two months ago. Somehow it didn't get to my mailbox. Found it on the web. I would like to revisit this question.

I think I understood your explanation. Our proposal is to add an ignore_multipaths section to multipath.conf that looks like the following:

ignore_multipaths
{
    name "flashgrid*"
}

This example should prevent multipathd from touching any DM devices with names starting with 'flashgrid'
The justification is that this will allow custom implementations of multipath management that also use dmsetup and that can co-exist on the same system with multipathd.

Is this possible to do? We will be happy to do testing.

Thank you!
-Artem


________________________________

  *   From: "Benjamin Marzinski" <bmarzins redhat com>
  *   To: device-mapper development <dm-devel redhat com>
  *   Subject: Re: [dm-devel] multipathd removing DM devices that don't belong to it
  *   Date: Mon, 22 Jun 2015 11:04:38 -0500

________________________________

On Tue, Jun 16, 2015 at 10:02:23PM +0000, Artem Danielov wrote:

>    Hello,

>

>    Looking for an advice on whether this is an expected behavior or a bug.

>

>    device-mapper-multipath-0.4.9-77.el7.x86_64

>

>

>

>    When multipathd service starts it will remove any DM devices with

>    multipath target, even if the underlying devices are blacklisted.

>

>    We are trying to use dmsetup directly  to implement custom multipath

>    management logic separate from multipathd. But unfortunately if multipathd

>    is present and enabled it removes DM devices with multipath target that we

>    create.

>

>

>

>    Is this a bug?



I don't know if I'd call it a bug. It is certainly how multipath is

designed to work.  The issue is this.  When you start multipathd up do a

reconfigure.  It doesn't know if the configuration has changed. So, if

there are devices configured and it doesn't think they should be, it

assumes that you've changed your configuration, and you'd like it to use

your current configuration, which means removing devices that no longer

are allowed.



I don't see any way of making this work, without adding a section to the

multipath.conf file to ignore devices with certain wwids entirely (which

is different from blacklisting them).



-Ben



>

>

>

>    Thanks for your help!

>

>

>

>    Artem Danielov | Chief Technology Officer | FlashGrid Inc. |

>    [1]artem flashgrid io | +1-503-568-5249

>

>

>

> References

>

>    Visible links

>    1. mailto:artem flashgrid io



> --

> dm-devel mailing list

> dm-devel redhat com

> https://www.redhat.com/mailman/listinfo/dm-devel




[-- Attachment #1.2: Type: text/html, Size: 13201 bytes --]

[-- Attachment #2: Type: text/plain, Size: 0 bytes --]

multipathd removing DM devices that don't belong to it

[Artem Danielov]

[-- Attachment #1.1: Type: text/plain, Size: 662 bytes --]

Hello,
Looking for an advice on whether this is an expected behavior or a bug.
device-mapper-multipath-0.4.9-77.el7.x86_64

When multipathd service starts it will remove any DM devices with multipath target, even if the underlying devices are blacklisted.
We are trying to use dmsetup directly  to implement custom multipath management logic separate from multipathd. But unfortunately if multipathd is present and enabled it removes DM devices with multipath target that we create.

Is this a bug?

Thanks for your help!

Artem Danielov | Chief Technology Officer | FlashGrid Inc. | artem@flashgrid.io<mailto:artem@flashgrid.io> | +1-503-568-5249


[-- Attachment #1.2: Type: text/html, Size: 2805 bytes --]

[-- Attachment #2: Type: text/plain, Size: 0 bytes --]

Re: multipathd removing DM devices that don't belong to it

[Benjamin Marzinski]

On Tue, Jun 16, 2015 at 10:02:23PM +0000, Artem Danielov wrote:
>    Hello,
> 
>    Looking for an advice on whether this is an expected behavior or a bug.
> 
>    device-mapper-multipath-0.4.9-77.el7.x86_64
> 
>     
> 
>    When multipathd service starts it will remove any DM devices with
>    multipath target, even if the underlying devices are blacklisted.
> 
>    We are trying to use dmsetup directly  to implement custom multipath
>    management logic separate from multipathd. But unfortunately if multipathd
>    is present and enabled it removes DM devices with multipath target that we
>    create.
> 
>     
> 
>    Is this a bug?

I don't know if I'd call it a bug. It is certainly how multipath is
designed to work.  The issue is this.  When you start multipathd up do a
reconfigure.  It doesn't know if the configuration has changed. So, if
there are devices configured and it doesn't think they should be, it
assumes that you've changed your configuration, and you'd like it to use
your current configuration, which means removing devices that no longer
are allowed.

I don't see any way of making this work, without adding a section to the
multipath.conf file to ignore devices with certain wwids entirely (which
is different from blacklisting them).

-Ben

> 
>     
> 
>    Thanks for your help!
> 
>     
> 
>    Artem Danielov | Chief Technology Officer | FlashGrid Inc. |
>    [1]artem@flashgrid.io | +1-503-568-5249
> 
>     
> 
> References
> 
>    Visible links
>    1. mailto:artem@flashgrid.io

> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel