[dm-devel] [PATCH 09/10] add disable_changed_wwids option

Tue Feb 28 12:27:27 UTC 2017

Hi,

 everyone

       In my testing in the use of 3Par storage device, when a LUN changes LUN number

 multipathd can not receive the uevent and can not disable access to the device.

 but for HP 6300 storage device, it can receive the uevent and disable access to the device.

So I think 3Par storage device don't support the case.

Now I don't have a right way to deal with the case. Thanks for your advise.

root at ubuntu98:~# udevadm monitor
monitor will print the received events for:
UDEV - the event which udev sends out after rule processing
KERNEL - the kernel uevent
KERNEL[68031.677399] change   /devices/virtual/block/dm-1 (block)
UDEV  [68031.711148] change   /devices/virtual/block/dm-1 (block)
KERNEL[68032.678563] change   /devices/virtual/block/dm-1 (block)
UDEV  [68032.705265] change   /devices/virtual/block/dm-1 (block)
KERNEL[68033.681120] change   /devices/virtual/block/dm-1 (block)
UDEV  [68033.709744] change   /devices/virtual/block/dm-1 (block)
KERNEL[68035.682421] change   /devices/virtual/block/dm-1 (block)
KERNEL[68051.693362] change   /devices/virtual/block/dm-2 (block)
UDEV  [68051.722144] change   /devices/virtual/block/dm-2 (block)
KERNEL[68052.694393] change   /devices/virtual/block/dm-2 (block)
KERNEL[68052.694761] change   /devices/virtual/block/dm-2 (block)
UDEV  [68052.721103] change   /devices/virtual/block/dm-2 (block)
root at ubuntu98:~# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04 LTS
Release:        16.04
Codename:       xenial

________________________________
All the best wishes for you.
zhangguanghui

From: dm-devel-bounces at redhat.com<mailto:dm-devel-bounces at redhat.com>
Date: 2016-11-04 23:32
To: Hannes Reinecke<mailto:hare at suse.de>
CC: dm-devel at redhat.com<mailto:dm-devel at redhat.com>
Subject: Re: [dm-devel] [PATCH 09/10] add disable_changed_wwids option

On Sun, Oct 30, 2016 at 02:54:14PM +0100, Hannes Reinecke wrote:
> On 10/29/2016 04:55 AM, Benjamin Marzinski wrote:
> >If a LUN on a storage device gets remapped while in-use by multipath,
> >it's possible that the multipath device will continue writing to this
> >new LUN, causing corruption.  This is not multipath's fault (users
> >should go remapping in-use LUNs), but it's possible for multipath to
> >detect this and disable IO to the device. If disable_changed_wwids
> >is set to "yes", multipathd will detect when a LUN changes wwids when it
> >receives the uevent for this, and will disable access to the device
> >until the LUN is mapped back.
> >
> >Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
> >---
> > libmultipath/config.c    |  1 +
> > libmultipath/config.h    |  1 +
> > libmultipath/defaults.h  |  1 +
> > libmultipath/dict.c      |  4 ++++
> > libmultipath/discovery.c | 15 +++++++--------
> > libmultipath/discovery.h |  1 +
> > libmultipath/structs.h   |  1 +
> > multipathd/main.c        | 32 ++++++++++++++++++++++++++++++++
> > 8 files changed, 48 insertions(+), 8 deletions(-)
> >
> Hmm. Not sure if the really buys us anything. By the time we process the
> uevent it might already be too late, and I/O might already have been written
> to that device.
> I do agree on the warning, though.

I have taken some pains to try to explain this short-coming to the
customer who filed this bugzilla. The good news is that in practice, the
device ususally goes down when you are remapping the LUN, and you
disable the device before it ever comes back.  In my testing, I wasn't
able to actually ever write to the wrong device with
disable_changed_wwids enabled, but I do agree that you have the
potential to race here.

-Ben

>
> Cheers,
>
> Hannes
> --
> Dr. Hannes Reinecke                 zSeries & Storage
> hare at suse.de                        +49 911 74053 688
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
> GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
>
> --
> dm-devel mailing list
> dm-devel at redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel

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