MFI and passthrough

[Doug Ambrisko]

Scott Long writes:
| Doug Ambrisko wrote:
| > Scott Long writes:
| > | The passthrough interface is really only meant for doing management
| > | tasks like SMART monitoring and firmware flashes.  I've also seen it
| > | used for low-duty devices like tape drives.  I do not recommend using it
| > | to directly control disks in a primary fashion.  However, since this is
| > | open source, I won't prevent you from trying =-)  Try the following
| > | patch:
| > | 
| > | --- mfi_cam.c   12 Oct 2007 16:52:55 -0000      1.3
| > | +++ mfi_cam.c   31 Oct 2007 03:42:25 -0000
| > | @@ -344,9 +344,11 @@
| > |                          command = ccb->csio.cdb_io.cdb_bytes[0];
| > |                  if (command == INQUIRY) {
| > |                          device = ccb->csio.data_ptr[0] & 0x1f;
| > | +#if 0
| > |                          if ((device == T_DIRECT) || (device == 
| > | T_PROCESSOR))
| > |                                  csio->data_ptr[0] =
| > |                                       (device & 0xe0) | T_NODEVICE;
| > | +#endif
| > |                  }
| > |                  break;
| > |          }
| > 
| > BTW, it works great in this mode if you know what you are doing :-)
| 
| Can you explain what that means?  I recommend against it because it's
| not a well-tested configuration either in FreeBSD or in Dell.  It's not
| clear, at least to me, how basic things like i/o errors get handled; 
| does SCSI sense data get consumed by the controller firmware, or is it
| passed through to the OS without problem?

That's what the "know what you are doing" comes in.  It should only
be used by people that know what they want and willing to take the
risks.  There are a bunch of pit falls like blowing up your RAID by
messing with disks under the RAID controller.  It seems to survive
a few failures but I haven't done exhaustive testing.  I did run into
an issue with one version of 7-current in which a one bad drive
would trip up a boot since a mfi command didn't complete.  Upgrading
to a newer 7-current solved that problem.  I should test out a bunch
of our bad disks with it but haven't had the time for that.

Doug A.