[dm-devel] Re: [BUG] dm-mpath and scsi persistent reservation

[Christophe Varoqui]

It seems to me the device handler infrastructure proposes to translate
scsi error codes from requests generated by the device handler itself. I
don't know how we can detect a reservation conflict from a device
handler without submitting a dangerous write io.

I don't see how we could use a device handler to translate an scsi error
code from a write io submitted to the multipath device map. Do you ?

Regards,
cvaroqui
> 
> The SCSI Hardware handler is created for devices with special needs.
> It is available in 2.6.27. One can be written for any device to
> translate the scsi sense code to a different error code that the dm
> understands. Is this something that coule help this situation ?
> 
> Have a look at drivers/scsi/device_handler directory.
> 
> Hope this helps,
> 
> chandra
> On Tue, 2008-10-21 at 23:19 +0200, Christophe Varoqui wrote:
> > Hi,
> > 
> > the dm-mpath multipathing driver enqueues write ios returned by
> > the scsi layer with a "reservation conflict" error (on assymetric
> > storage controllers, like Clariion, where queue_if_no_path is
> > enabled).
> > 
> > This is wrong, and a potent data-corrupter : wio sent to a reserved
> > scsi device should never be retried on this same device.
> > 
> > Can someone advise on a viable solution for this problem ? I
> > understand the Device Mapper being a block remapper, it is not
> > expected to receive scsi errors directly ... but maybe some kind of
> > translation might be acceptable. Or is there hope in the
> > request-based remapper ?
> > 
> > Jens, James, Alasdair, ... as maintainers of the involved
> > subsystems, would you care to give some advise on the issue.
> > 
> >