Re: RFC: GEOM MULTIPATH rewrite

On 10/31/11 22:10, Alexander Motin wrote:
> Attempt to fix some GEOM MULTIPATH issues made me almost rewrite it. So
> I would like to present my results and request for testing and feedback.
> 
> The main changes:
>  - Improved locking and destruction process to fix crashes in many cases.
>  - Improved "automatic" configuration method to make it safe by reading
> metadata back from all specified paths after writing to one.
>  - Added provider size check to reduce chance of conflict with other
> GEOM classes.
>  - Added "manual" configuration method without using on-disk metadata.
>  - Added "add" and "remove" commands to manage paths manually.
>  - Failed paths no longer dropped from GEOM, but only marked as FAIL and
> excluded from I/O operations.
>  - Automatically restore failed paths when all others paths are marked
> as failed, for example, because of device-caused (not transport) errors.
>  - Added "fail" and "restore" commands to manually control FAIL flag.
>  - GEOM is now destroyed on last provider disconnection. IMHO it is
> right to do if device was completely removed.
>  - Added optional Active/Active mode support. Unlike Active/Passive
> mode, load evenly distributed between all working paths. If supported by
> device, it allows to significantly improve performance, utilizing
> bandwidth of all paths. It is controlled by -A option during creation.
> Disabled by default now.
>  - Improved `status` and `list` commands output.

Here is slightly updated version:
http://people.freebsd.org/~mav/gmultipath5.patch

Changes from previous:
 - "label" command was made to check metadata on other specified devices
after writing to the first one and warn if something wrong there.
 - "add" command was allowed for devices created using automatic method.
It may be useful in cases when some paths are temporary not operational
and can't even read metadata. In such case they could be added manually
and marked failed until their time will come.
 - Load balancing in Active/Active mode slightly improved: if all paths
have equal load, do round-robin between them.

-- 
Alexander Motin