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In a Serengeti system with firmware 5.20.1 or later and the new Version 2 Repeater Board (Repeater Board V2), USIV+ hardware resources can be configured as a single partition or divided into two physically separate partitions.  A partition does not share hardware with any other partition.

Additionally, a partition can be further divided into two domains.  Domains do share hardware resources.  This issue will effect both domains in the partition when the partition is divided into 2 domains.  When setting up the platform, if the user indicates they will be deploying USIV+ boards in parition0 they will be asked:

• Will you deploy both domains A and B in partition0? [false]:

If they indicate they will be deploying USIV+ boards in Partition1 they will be asked:

• Will you deploy both domains C and D in partition1? [false]:

Once the user answers true to these questions the performance impact is placed into effect for all domains (including all CPU types) that operate in this partition, even if there is only one domain installed and active.

The performance restriction addressed in this domain can be removed by using "setup platform" again in the future and answering these questions with false and removing the support for 2 domains in the partition. This issue will not be relevant to a domain in the partition adjacent to the dual domain partition unless that partition is also is divided into 2 domains.

Domains are labeled A,B,C,D. A and B share a partition, and C and D share a partition. The table below shows which domains may experience these issues and which will not:

DOMAINS		      DOMAINS
AVAILABLE	      EFFECTED
A B C D
--------------------------------
0 0 1 0	              NONE
0 0 1 1               domain C/D
1 0 0 0               NONE
1 0 1 0               NONE
1 0 1 1	              domain C/D
1 1 0 0	              domain A/B
1 1 1 0	              domain A/B
1 1 1 1	              domain A/B and domain C/D

When configuring Serengeti servers into 2 domains within a single partition the memory and response bus bandwith are cut in half.  This can result in a slight performance degradation in some applications (such as those that do a lot of memory transactions).  As a result of the implementation of the UltraSparc IV+ processor, the performance impact of utilizing 2 domains within a single partition may be more noticeable when the partition contains UltraSparc IV+ processors than what has been seen in the past with the slower UltraSparc IV and UltraSparc III processors.

The performance impact will be more significant on single board domains and may also be noticeable on very lightly loaded domains regardless of the attributes of the load.

When mixed with UltraSparc IV+ processors within a partition, the performance impact of Ultrasparc IV and UltraSparc III processors may be more noticeable than the impact on the Ultrasparc IV+ processors.

All system boards are affected when UltraSparc IV+ boards are present in a dual domain partition.  Use "prtdiag -v" on each domain or look at prtdiag_-v.out in the Explorer on each domain.  If US-IV+ is specified in the CPU Impl. column, then UltraSparc VI+ boards are present and the partition is susceptible to the issues discussed in this FIN.  Below is a sample prtdiag -v.out file from an Explorer showing the boards with US-IV+ processors:

            CPU      Run    E$   CPU      CPU
FRU Name    ID       MHz    MB   Impl.    Mask
----------  -------  ----  ----  -------  ----
/N0/SB4/P0   16,528  1500  32.0  US-IV+   2.1
/N0/SB4/P1   17,529  1500  32.0  US-IV+   2.1
/N0/SB4/P2   18,530  1500  32.0  US-IV+   2.1
/N0/SB4/P3   19,531  1500  32.0  US-IV+   2.1

For the E4900 and 4800 it is strongly recommended that two partitions should be used whenever there are two domains.  This will provide physical isolation of the two domains, protecting the one from the other in the event of a failure, avoid the 50% degradation of the snooping bandwidth as well as avoid the performance issues when using USIV+ boards within a partition.

Note: The issues and recommendations are the same for the E6900 and E6800 when using two domains.

When setting up a partition to initially run only one domain when there is a desire or a potential desire to add a second domain in the future, the customer has two options to consider:

1. Answer false to the question about deploying both domains in the partition.  This avoids the performance issue described in this document while there is only one domain but will require a platform outage to use setup platform to answer the questions true before the second domain can be added.
2. Answer true to the question about deploying both domains in the partition. This avoids the need for a platform outage to deploy the second domain but will result in the performance restriction being applied to the single domain from the beginning.

Be aware of the issues described in this document and set customer expectations appropriately.

When performance is an important issue, discourage the use of multiple domains within a partition.

When multiple domains in a single partition are required by the customer, discourage mixing UltraSparc IV+ with other types of CPU's within the partition.

•  Modified Synopsis.

• Updated synopsis with capital letters.

• Manual: 819-6577-10 SunFire Midrange Systems Firmware 5.20.1 Release Notes

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