Linux Cluster using shared scsi

[Roets, Chris]

> Problem :
> install two Linux-system with a shared scsi-bus and storage on that shared
> bus.
> suppose :
> system one : SCSI ID 7
> system two : SCSI ID 6
> shared disk : SCSI ID 4
> 
> By default, you can mount the disk on both system.  This is normal
> behavior, but
> may impose data corruption.
> To prevent this, you can SCSI-reserve a disk on one system.  If the other
> system
> would try to access this device, the system should return an i/o error due
> to the reservation.
> This is a common technique used in
> - Traditional Tru64 Unix ase clustering
> - Tr64 Unix V5 Clustering to accomplish i/o barriers
> - Windows-NT Clusters
> - Steel-eye clustering
> The reservation can be done using a standard tool like scu
> 
> scu -f /dev/sdb
> scu > reserve device
> 
> On Linux, this works fine under Kernel version 2.2.16.
> Below is the code that accomplish this
> /usr/src/linux/drivers/scsi/scsi_obsolete.c in routine scsi_old_done
>             case RESERVATION_CONFLICT:
>                 printk("scsi%d (%d,%d,%d) : RESERVATION CONFLICT\n",
>                        SCpnt->host->host_no, SCpnt->channel,
>                        SCpnt->device->id, SCpnt->device->lun);
>                 status = CMD_FINISHED; /* returns I/O error */
>                 break;
>             default:
> As of kernel version 2.2.18, this code has changed, If a scsi reserve
> error
> occurs, the device driver does a scsi reset.  This way the scsi
> reservation is
> gone, and the device can be accessed.
> /usr/src/linux/drivers/scsi/scsi_obsolete.c in routine scsi_old_done 
>             case RESERVATION_CONFLICT:
>                 printk("scsi%d, channel %d : RESERVATION CONFLICT
> performing"
>                        " reset.\n", SCpnt->host->host_no, SCpnt->channel);
>                 scsi_reset(SCpnt, SCSI_RESET_SYNCHRONOUS);
>                 status = REDO;
>                 break;
> 
> Fix : delete the scsi reset in the kernel code
>             case RESERVATION_CONFLICT:
> /* Deleted Chris Roets
>                 printk("scsi%d, channel %d : RESERVATION CONFLICT
> performing"
>                        " reset.\n", SCpnt->host->host_no, SCpnt->channel);
>                 scsi_reset(SCpnt, SCSI_RESET_SYNCHRONOUS);
>                 status = REDO;
> next four lines added */
>                 printk("scsi%d (%d,%d,%d) : RESERVATION CONFLICT\n",
>                        SCpnt->host->host_no, SCpnt->channel,
>                        SCpnt->device->id, SCpnt->device->lun);
>                 status = CMD_FINISHED; /* returns I/O error */
>                 break;
> 
> and rebuild the kernel.
> 
> This should get the customer being able to continue
> 
	Questions  :
> - why  is this scsi reset done/added as of kernel version 2.2.18
> - as we are talking about an obsolete routine, how is this accomplished 
>  in the new code and how is it activated.  
> 
> 
> Chris