James Bottomley [James.Bottomley@steeleye.com] wrote:
> jeremy@classic.engr.sgi.com said:
> > For example, in Fibrechannel using class 3 (the usual)
>
> > send command (command frame corrupted; device does not receive)
> > send barrier (completes normally)
> > ... (lots of time goes by, many more commands are processed)
> > timeout original command whose command frame was corrupted
>
> This doesn't look right to me from the SCSI angle I don't see how you can get
> a successful disconnect on a command the device doesn't receive (I take it
> this is some type of Fibre magic?). Of course, if the device (or its proxy)
> does receive the command then the ordered queue tag implementation requires
> that the corrupted frame command be processed prior to the barrier, this
> isn't optional if you obey the spec. Thus, assuming the processor does no
> integrity checking of the command until it does processing (this should be a
> big if), then we still must get notification of the failed command before the
> barrier tag is begun. Obviously, from that notification we do then race to
> eliminate the overtaking tags.
In FC class 3 if you are logged into a port then notice of this loss
doesn't happen until a upper level timeout occurs (ULTP?). The loss can
happen prior to the command reaching the device (i.e. the switch can
drop the frame). If a corrupted frame makes it to the device it will be
discarded as there is not much it can do with a frame containing unreliable
data. In FC class 2 frames are ack'd so the recovery can be much more
responsive.
-Mike
-- Michael Anderson andmike@us.ibm.com- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Sat Sep 07 2002 - 22:00:22 EST