[dm-devel] Setting up a multipath device

[Christophe Varoqui]

> 
>    1. Was it wrong to run 'multipath 2 round-robin 1 0 /dev/sda
>       round-robin 1 0 /dev/sdb'?

The multipath command just don't understand these parameters.
This is a map as seen by the DM kernel driver. You can feed it to
dmsetup(8), not to multipath(8).

>    2. If I don't supply any parameters, how does the dm know which
>       devices are the same physical device (that /dev/sda & /dev/sdb are
>       the same physical device)?

Because it scans the paths for unique LU ids, then coalesce.

>    3. How are the priority groups defined if no parameters are supplied?

User defines, through config file.

>    4. What is the timeout for a device that has failed? When does the dm
>       move to the next priority group?
> 
When secondary PG priority becomes higher than the active PG priority,
modulo user-define delay or user-define disabling.

Or when all paths in the active PG have failed.

Regards,
cvaroqui