iSCSI: Aggregation tags in SendTargets

[Mark Bakke <mbakke@cisco.com>]

During the interim meeting, we had discussed a proposal to
add an aggregation tag to the SendTargets response, indicating
which (if any) target addresses supported multiple connections
per session, and which groups of addresses an initiator could
hope to aggregate a session across.

Aggregation tags were generally well-received; a small modification
to the proposed method also allows an initiator to know whether
a single address supports multiple connections per session just
by itself.

Here is the section that would go into the NDT document.

--

(This would be added to section 4.2, right before the vendor-specific
paragraph at the end):


  If an iSCSI target supports multiple connections per session,
  it must indicate this by including an aggregation tag after each 
  address, in the form of

    TargetAddress=address,tag

  Where "tag" is an ASCII, alpha-numeric string indicating an address 
  group.  Within a single session, a connection may be requested to any
  combination of TCP addresses that have the same tag.  If an address
  supports multiple connections per session, but does not support
  spanning a session across other addresses, it will have its own
  tag.
  
  Here is an example:

    TargetName=fqn.com.acme.diskarray.sn.8675309
    TargetAddress=10.1.0.45:3000,1
    TargetAddress=10.1.1.46:3000,1
    TargetAddress=10.1.0.47:3000,2
    TargetAddress=10.1.1.48:3000,2
    TargetAddress=10.1.1.49:3000
    TargetAddress=10.1.1.50:3000,3
    TargetAlias=Oracle tables

  In this example, any of the target addresses can be used to reach
  the same target.  A single-connection session can be established
  to any of these TCP addresses.  A multiple-connection session could span
  addresses .45 and .46, or .47 and .48, but cannot span any other
  combination.  A TargetAddress without a tag (.49) cannot be combined
  with any other address within the same session.  A TargetAddress
  with a tag that is not shared with other addresses supports multiple
  connections per session, but all connections must be to the same
  address.

  To make this work, there are a few rules to follow:

  A target that does not support spanning sessions across multiple addresses
  MUST NOT include the tags.

  A target that is accessible via multiple TCP addresses SHOULD include
  all TCP addresses in a SendTargets response.

  A target with multiple TCP addresses that supports a session spanning
  multiple TCP addresses MUST indicate TCP address groups using aggregation
  tages in a SendTargets response.

  Aggregation tags have no meaning or persistence beyond a particular
  SendTargets response.



-- 
Mark A. Bakke
Cisco Systems
mbakke@cisco.com
763.398.1054