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Document Information
| Document Number: | 431746586 |
| Functional Area: | System i Integration with BladeCenter and System x |
| Subfunctional Area: | iSCSI |
| Sub-Subfunctional Area: | General |
| OS/400 Release: | V5R4M0 |
| Product: | OS/400 BASE (5722SS100) |
| Product Release: | N/A |
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Document Title
Problems with Blades Connected to System i via Server Connectivity Module
Document Description
External ports on a Server Connectivity Module (SCM) for IBM® BladeCenter® are trunk ports that are intended to connect to other switches. The SCM's default configuration assumes that all of its external ports connect to a single switched network, such as a single external switch. It uses a link aggregation protocol known as EtherChannel to makes decisions about which of its external ports to use for sending, based on frame contents.
If you connect multiple external ports of an SCM directly to iSCSI HBAs in an IBM® System i™ without an external switch, some or all of the blades might have a problem from the following list:
| o | Boot failure |
| o | Inability to access storage provided via the System i iSCSI HBA |
| o | Virtual Ethernet adapters in a link down state |
Use one of the following methods to allow SCM to successfully connect to the System i iSCSI HBAs without external switches; however, there are restrictions.
Solution 1: Use only one SCM external port. Multiple blades share a single 1G bps connection and single network server host adapter (NWSH). This solution works with the SCM's default configuration.
Solution 1 has the following restrictions:
| o | There must not be an active link on the other 5 external ports (such as another varied-on NWSH or target iSCSI HBA). |
| o | Storage spaces for all blades connected via this SCM must be linked to the same NWSH. There is a hard limit of 8 network server descriptions (NWSDs) per NWSH and a practical limit that is determined by the total workload that you want to run over the bandwidth of a single iSCSI HBA. |
| o | Each NWSD/blade can access only one NWSH through an SCM. |
Solution 2: Configure the SCM to act as 6 small switches with one external access port per switch.
This solution requires SCM configuration changes using the following procedure:
| 1 | Access the SCM's BBI (Browser Based Interface) by following the instructions starting on page 64 of the SCM user guide, which is available at the following Web site: http://www-1.ibm.com/support/docview.wss?rs=0&q1=39Y9324&uid=psg1MIGR-64190&loc=en_US&cs=utf-8&cc=us&lang=en |
| 2 | Use Port Group Mapping in the BBI to set each of the six external ports to a different group number (1 - 6). Similarly, assign each blade slot to a group number (1 - 6) that is consistent with how the NWSHs/external ports are to be shared among the blades. If there is a dedicated NWSH for a blade, configure a group that includes just the appropriate external port and blade. Each group is logically a separate small switch. |
| o | Each NWSD/blade can access only one NWSH through an SCM. |
| o | Hot spare of a blade or a target iSCSI HBA requires more steps. In addition to the usual steps, it is necessary to use the SCM BBI to ensure that blades and external ports are in appropriate port groups at hot spare time. This is because hot spare does not work across different SCM port groups. |
For information regarding switch requirements, refer to the following article:
http://www-03.ibm.com/systems/i/bladecenter/iscsi/switches.html.
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