Dell EMC Unity: AIX Boot from Dell EMC Unity fails with Method Error using powerpath (User Correctable)

Customer changed from a VNX5400 to a Dell EMC Unity 300F, using the the same Powerpath version and AIX and ODM versions. 

AIX LPAR'S connected to Dell EMC Unity arrays cannot boot from SAN, but the same AIX LPARS connected to the VNX series arrays can boot up just fine.

Error message received on AIX:

Method error (/usr/lib/methods/cfgefscsi -2 -l fscsi1 ):0514-061 Cannot find a child device

This is a timing issue caused by newer, faster switch hardware.  The older Gen 4 switches did not experience this issue, but the newer, faster Gen 5 switches do.

The Host initiator logs in to the fabric and discovers the boot device.  It then logs out of the fabric and logs back in again.  On the newer hardware, this second login is occurring before the switch can send a RSCN to the fabric to clear out the previous login, and therefore the second login is assigned a different FCID in the switch.

When the same WWN attempts to log in to the array with a new FCID, the login is rejected because that WWN is already logged in.

Fix:
It is unknown whether or not IBM will address the timings of the fabric logout/login.

Workaround:
The issue can be worked around by enabling WWN-based Persistent PID in the switch.  When this is set, a WWN will always be assigned the same FCID when logging out and logging back in again, thus avoiding the issue altogether.  In order to enable this setting, the switch must have 8-Bit Dynamic Area Mode enabled, which is performed through the switch's configure menu, which requires the switch to be disabled in order to set.  Therefore, making this change is an offline event.  Smaller DCX switches do not support Dynamic Area Mode; in such a case, the offline event is not needed.

WWN-Based Persistent PID -- When enabled, this feature supports both dynamic and static WWN-based PID assignment. In dynamic PID binding, the first area assigned to a device when it logs in is bound to the device WWN and remains persistent through subsequent logins. Every time the device logs into the switch, it is guaranteed to get the same PID. Alternately, you can use the wwn Address command to create a static WWN-based PID assignment. In either case, the WWN-based persistent PID feature must be enabled through configure. The feature is disabled by default; it is dependent on Dynamic Area Mode being enabled.  This feature can be enabled online if Dynamic Area Mode is already enabled.

Enable 8-bit Dynamic Area Mode -- When enabled, this feature supports Dynamic Area Mode in default partitions on the Brocade DCX-4S, DCX 8510-8, and DCX 8510-4. Dynamic Area Mode is disabled by default. When enabled, Dynamic Area Mode supports both static and dynamic area assignment. Use the portAddress command to perform a static assignment of an area to a given port. In Dynamic Area Mode, areas are dynamically assigned to the ports (up to a 255 limit). Port area assignments are persistent; however, disabling Dynamic Area Mode with configure resets the area assignments.  This feature is set through the configure menu, and requires the switch to be in disabled mode in order to set.

There are different address modes on the DCX platforms because of the port counts. On DCX 6520 switches, for example, you do not need to disable the switch and change the address mode because the port count is less than 255, so no dynamic mode is available.  You can enable WWN-Based Persistent PID online.

For corresponding information on this recommendation, please refer to the DELL/EMC Fibre Channel SAN Technologies guide for specifies that speak to the recommendation that port persistence be enabled as a best
practice, available on E-lab Navigator (ELN)

https://elabnavigator.emc.com/vault/pdf/FC_SAN.pdf

Refer to page 96, "Configure FC switches", step 2g, "Switch PID Format" parameter value of 1.

Also see:
Brocade Defect Article Number : 000008158
Title : Host fails to boot from SAN when attached to ports with FC ID ALPA of 0x40 or 0xC0


- AIX levels: 7100-04-02-1614
 PowerPath (c) Version 6.0 SP 1 (build 132)
- ODM version:
 EMC.CLARiiON.aix.rte       6.0.0.5  COMMITTED  EMC CLARiiON AIX Support
 EMC.CLARiiON.fcp.rte       6.0.0.5  COMMITTED  EMC CLARiiON FCP Support
 EMCpower.MgmtComponent     6.0.1.0  COMMITTED  PowerPath Management
 EMCpower.base              6.0.1.0  COMMITTED  PowerPath Base Driver and
 EMCpower.migration_enabler
 EMCpower.mpx               6.0.1.0  COMMITTED  PowerPath Multi_Pathing
- VIOS level:
2.2.4.21
- DS-6520R-B switch - FC port set to AUTO and negotiating @ 8GB speed (max speed of the HBA card on IBM System)
- IBM Power8 System, Model/Type - S814/8286-41A, FW level: FW840.30 (SV840_139)
Unity 300F array (SPA0,0). 
Brocade 6510B with 7.4.0a code on it.
- Dell EMC Unity LUN: 65GB, Thin

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