RE: Keep-alive traffic (was iSCSI: more on StatRN)

["Y P Cheng" <ycheng@advansys.com>]

> From: Douglas Otis [mailto:dotis@sanlight.net]
> Sent: Tuesday, October 31, 2000 11:03 AM
>
> It is not as simple as that.  StatRN does not provide a deterministic
> timeout for a connection failure indication.  As such, it should not be
> relied upon to determine a failed connection.  Even with
> keepalive, the TCP
> timeout will still be too long for useful connection recovery
> should status
> be pending.  It would be desirable to prevent a reset and overlapping
> recoveries.  As such, for a connection failure detection to be useful, it
> must be relatively quick.  The SCSI layer should know little about the
> underlying transport so the transport must be pro-active in responding to
> transport failure.  Repetitive probes every 10 seconds could satisfy
> detection requirements while status is pending.  This would also
> provide the
> target early notice of a client failure as communication while not idle
> would be deterministic.

You are 100% correct.  If we have a table defining all possible error, not
receiving the PDU with the right StatRN is one.  The question becomes how
long do you wait?  I also understand your position in using ping every 10
seconds so we don't need to wait four minutes to decide if TCP connection is
gone.