Bug#510911: multipath-tools: bad side effects with FC devices

[Guido Günther]

Hi Vincent,
On Wed, Jan 21, 2009 at 10:43:30AM +1100, Vincent.McIntyre at csiro.au wrote:
[..snip..] 

This part doesn't apply here. Could you just send me the full
multipath-tools.README.Debian. I'll replace the current one as is and do
some minor touch ups.
Thanks for your work!
 -- Guido


> diff -urN -ruN multipath-tools-0.4.8.orig/debian/multipath-tools.README.Debian multipath-tools-0.4.8/debian/multipath-tools.README.Debian
> --- multipath-tools-0.4.8.orig/debian/multipath-tools.README.Debian	2009-01-12 08:32:37.197654000 +1100
> +++ multipath-tools-0.4.8/debian/multipath-tools.README.Debian	2009-01-21 10:40:19.417523000 +1100
> @@ -1,16 +1,65 @@
> -To enable booting from multipathed devices install multipath-tools-boot
> +Additional information for users of multipath-tools from Debian.
> +
> +What are these weird numbers in /dev/mapper?
> +============================================
> +Modern Fibre-Channel connected storage devices are identified by
> +World-Wide-Numbers. If multipath-tools detects one of these devices,
> +it uses that as the default identifier in /dev/mapper.
> +If you want multipath-tools to use easier-to-read names, set
> +  user_friendly_names = yes
> +in the 'defaults' section of /etc/multipath.conf.
> +
> +Where did my FC-connected filesystem go?
> +========================================
> +If you were previously mounting a device connected to your system by
> +Fibre Channel and then installed multipath-tools, you need to change
> +the way you mount the device. The device must now be accessed using
> +the identifier by which device-mapper knows it.
> +
> +For example if you have in /dev/mapper a file like this:
> +   brw-rw---- 1 root disk 254,  8 2009-01-05 14:35 /dev/mapper/36000393000007d3901000000fef00a2d
> +
> +then you can mount the filesystem like this:
> +  mount /dev/mapper/36000393000007d3901000000fef00a2d /mnt
> +or this
> +  mount /dev/disk/by-id/scsi-36000393000007d3901000000fef00a2d /mnt
> +You should prefer the latter, as this will work whether or not 
> +multipath-tools is installed.
> +
> +Note that with multipath-tools installed you cannot use the device's node
> +in /dev, e.g.
> +  mount /dev/sdc1 /mnt
> +  mount: /dev/sdc1 already mounted or /mnt busy
> +The device is 'busy' because it is part of a multipath map.
> +See the output of 'multipath -l' to confirm this.
> +
> +Preventing multipath-tools mapping any devices
> +==============================================
> +You may wish to prevent multipath-tools mapping any of your storage devices.
> +To do this replace the contents of /etc/multipath.conf with:
> +
> +  blacklist {
> +         devnode "*"
> +  }
> +
> +Booting from multipathed devices
> +================================
> +To enable booting from multipathed devices install the multipath-tools-boot
>  package. Be sure to update your bootloader configuration (e.g.
> -/boot/grub/menu.lst) to point to the multipathed root device afterwards. This
> -is either
> +/boot/grub/menu.lst) to point to the multipathed root device afterwards.
> +
> +By default this will be
> +
> +  /dev/mapper/<WWID>-part<N>
>  
> -/dev/mapper/<WWID>-part<N>
> +unless you use an alias in /etc/multipath.conf.
>  
> -if you don't use an alias in /etc/multipath.conf or
> +If you set user_friendly_names = yes in /etc/multipath.conf, the path
> +to the device will be
>  
> -/dev/mapper/mpath<X>-part<N>
> +  /dev/mapper/mpath<X>-part<N>
>  
> -when using user_friendly_names = yes in /etc/multipath.conf. Also remember to
> -run update-initramfs after making changes in multipath.conf so the updated
> -version get's included into the initramfs.
> +If you make changes in multipath.conf, remember to run update-initramfs
> +so the updated version of the configuration gets included in the initramfs.
>  
>   -- Guido Günther <agx at sigxcpu.org>  Tue, 20 Feb 2008 13:49:18 +0100