IBM-AUSTRIA - PC-HW-Support    30 Aug 1999

POOR SSA DISK WRITE PERFORMANCE

    Record number:       H166560
    Device:              D/T8650
    Model:               M
    Hit count:           UHC00000
    Success count:       USC0000
    Publication code:    PC50
    Tip key:
    Date created:        O99/05/05
    Date last altered:   A99/05/21
    Owning B.U.:         USA


Abstract: POOR SSA DISK WRITE PERFORMANCE

TEXT:

Poor SSA Disk write performance on Netfinity 7000 server or PC Server 704.

SYMPTOMS:

A performance degradation has been found on the Netfinity 7000 and PC Server 704 with respect to specific placement of PCI adapter cards.
The problem was originally found while performing a network based restore to SSA disk drives.
Any load where both disk and network traffic are occurring simultaneously would be affected.
The problem is caused by PCI Slot restrictions on the Netfinity 7000 and PC Server 704.

The degradation occurs when both conditions 1 and 2 are met:

1.  An SSA Adapter and a Network adapter exist on the same PCI bus.
2.  The SSA adapter or Network adapter is installed in slot-1 or slot-6.

    Further degradation may occur if both conditions 1 and 2 (above) are met, accompanied by either condition 3 or 4:

3.  If either adapter is installed in slot-6, slot-1 is occupied by another high performance PCI adapter.
4.  If either adapter is installed in slot-1, slot-6 is occupied by another high performance PCI adapter.

PROBLEM ISOLATION AIDS:

•  The system is any of the following IBM servers:

    a Netfinity 7000 server, Type 8651, any Model.
    a PC Server 704, Type 8650, any Model.

•  The system is configured with 1 to 4 Processors.
•  The system is configured with at least one of the following:

       IBM SSA RAID Adapter for PC Servers,              Option P/N 32H3811
       IBM SSA RAID Cluster Adapter for PC Servers,      Option P/N 96H9835
       IBM SerialRAID Adapter for PC Servers,            Option P/N 09L2084
       IBM Advanced SerialRAID/X Adapter for PC Servers, Option P/N 09L2123
   

•  The system's Diagnostics PASS.
•  The system's SSA Diagnostics PASS.
•  The system's Network Card Diagnostics PASS.
•  ANY Device Driver for the following adapters are affected:

    Any Network Adapter
    SSA

•  ANY Firmware for the following adapter are affected:
    Any Network Adapter
    SSA

•  NOS affected:

    OS/2 versions 3.0 or 4.0 at any fix pack level
    NetWare version 4.11 at any patch level
    NT versions 3.51 or 4.0 at any service pack level

WORKAROUND:

1.  Avoid the use of PCI slots-1 and slot-6 if possible.
2.  Always place like adapters on the same bus.
3.  Avoid combinations of Network and SSA adapters on the same bus if possible.
4.  If a Network and SSA adapter must be located on the same bus, do not place either in slot-1 or slot-6.

DETAILS:

The SSA adapter in PCI slot-1 or slot-6 will be affected by a High Performance PCI adapter in either of the two remaining slots of the respective PCI bus.
The SSA adapter will also be affected if the High Performance adapter is in slot-1 or slot-6 and the SSA adapter is on the same bus.
Lab tests have shown that the IBM EtherJet Adapter and the IBM ServeRAID adapter are two examples of "High Performance" adapters.
The sensitivity to slot-1 and slot-6 led to recommended slot placement of adapters.

Note: Three (3) of the same type of adapters on one bus (e.g. three (3) SSA adapters in slots 1, 2, and 3) do not exhibit this problem.

Netfinity 7000 and PC Server 704 Slot to Bus Mapping:

       Slot Number     Bus Number
            1              0
            2              0
            3              0
            4              1
            5              1
            6              1

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