[Linux-cluster] AW: GNBD multipath with devicemapper? -- possible solution

[Hansjoerg.Maurer at dlr.de]

Hi

I found a solution for the problem descriped below,
but I am not sure if it is the right way.

- importing the two gnbd's (wich point to the same device) from two servers
-> /dev/gnbd0 and /dev/gnbd1 on the client

- creating a multipath device with something like this:
echo "0 167772160  multipath 0 0 1 1 round-robin 0 2 1 251:0 1000 251:1 1000 " | dmsetup create dm0
 (251:0 ist the major:minor id of /dev/gnbd0)

- mounting the created device
eg:
mount -t gfs /dev/mapper/dm0 /mnt/lvol0

If I do a write on /mnt/lvol0 the gnbd_server task on both gnbd_servers start (with a noticeable speedup)

If one gnbd_server fails dm removes that path with the following log
kernel: device-mapper: dm-multipath: Failing path 251:0.

I was able to add it again with

dmsetup  message dm0 0  reinstate_path 251:0


I was able to deactivate a path manually with

dmsetup  message dm0 0  fail_path 251:0 

But I can not unimport the underlying gnbd

gnbd_import: ERROR cannot disconnect device #1 : Device or resource busy


Is there a way to remove a gnbd, which is bunndled in a dm-multipath device?
(might be necessary, if one gnbd server must be rebooted)

How can I reimport an gnbd on the client in state disconnected?
(I had to manually start 
gnbd_recvd -d 0  to do so)

Is the descriped solution for gnbd multipath the right one?

Thank you very much

Greetings from munich

Hansjörg






>Hi
>
>I am trying to set up gnbd with multipath.
>Accoding to the gnbd_usage.txt file, I understand, that this should work with
>dm-multipath.
>But unfortunatly only the gfs part of the setup is descriped there.
>
>Has anybody experiance with this setup, especially how to set up
>multipath with multiple /dev/gnbd* and how to setup the multipath.conf file
>
>
>Thank you very much
>
>Hansjörg Maurer
-- 
_________________________________________________________________

Dr.  Hansjoerg Maurer           | LAN- & System-Manager
                                |
Deutsches Zentrum               | DLR Oberpfaffenhofen
  f. Luft- und Raumfahrt e.V.   |
Institut f. Robotik             |
Postfach 1116                   | Muenchner Strasse 20
82230 Wessling                  | 82234 Wessling
Germany                         |
                                |
Tel: 08153/28-2431              | E-mail: Hansjoerg.Maurer at dlr.de
Fax: 08153/28-1134              | WWW: http://www.robotic.dlr.de/
__________________________________________________________________


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