Negotiating draining capability

The source LU can specify draining capability for itself and for its partner LU (target) when issuing a CNOS request. It would use DRAINL (SLCDRAL) and DRAINR (SLCDRAP), respectively.

The target LU cannot negotiate the draining capability of the source LU that makes the CNOS request. The target LU must accept what the source LU has specified. The target LU can negotiate the draining capability for its own side to indicate that it will not enable draining on the target side.

The source LU that issues the CNOS request can prevent draining on the target side by setting the value of the DRAINR parameter to NO in the CNOSsession limits control block.

The draining options for the target LU are shown in Table 1.

Table 1. Draining options for the target LU
Source Side LU (DRAINR in CNOS structure (SLCNS))	Target Side LU (DDRAINL in DEFINE structure (SLD))	Target Side Options
NO	YES	Cannot support draining
NO	NO	Cannot support draining
YES	NO	Negotiates draining support to NO and does not do draining
YES	YES	Supports draining

When the CNOS request applies to all mode names, a value of YES for the DRAINR parameter in the CNOS control block is ignored for a particular mode name if draining on the target side for that mode name is currently not enabled and the current session limit for that mode name is 0.