Re: Multipath command output - Help with understanding output

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On Tue, Oct 13, 2009 at 6:45 PM, Bryn M. Reeves <bmr@xxxxxxxxxx> wrote:
> On Tue, 2009-10-13 at 18:23 +0100, Dan Track wrote:
>> I've already got the following /dev/mapper/mpath0 and
>> /dev/mpath/3600c0ff000d7ba4f4575b24a01000000. Can you tell me how I
>> can reload the config and end up with /dev/mapper/san1?
>
> That's a little bit strange; normally you'd expect the /dev/mpath
> entries to follow the same naming as is used in /dev/mapper.
>
> That said, the symlinks in /dev/mpath are nothing but trouble and it is
> strongly advised that you don't use them for anything. The main problem
> is that they can at times get out-of-sync with the device-mapper status.
> This can lead to a range of problems such as failed booting (since the
> correct device names don't exist at the point they should in the boot
> process) to data corruption when a stale symlink ends up pointing to the
> wrong multipath device.
>
> This happens because the device nodes in /dev/mapper are managed by
> libdevmapper and so are updated in-sync with the state of the devices in
> the kernel but the symlinks are managed in userspace by udev and so
> there can be delays between the device-mapper's state changing and the
> corresponding symlinks getting updated.
>
>> Also when running pvcreate should I run
>>
>> pvcreate /dev/mapper/mpath0
>
> Always prefer the names in /dev/mapper when working with multipath
> devices.
>
> Regards,
> Bryn.
>
Many many thanks Bryn. I owe you one.

Thanks
Dan

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