Microsoft KB Archive/193142

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SCSI/PCI Bus Performance Affects Theater Server Stream Count

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Q193142

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The information in this article applies to:


 * Microsoft NetShow Theater Server version 3.0

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SYMPTOMS
This article details a potential SCSI and/or PCI bus bottleneck that can limit the streams per disk count, (as measured by the Theater Server Setup disk drive performance tests).

NetShow Theater Server Setup examines content disk drive performance, and then displays the results of this examination. When Setup completes the examination (which can take 20 minutes or longer for systems with many content drives), it displays the performance results for all disk drives on the video server. This helps to identify disk drives with substandard performance. If all the disk drives are identical, their performance is likely to be identical. A lower value on one drive or server may indicate a hardware problem.

NetShow Theater Server Setup sets the sustained transfer rate for all the hard disks to the lowest observed transfer rate. If you mix low- performance hard disks with high-performance hard disks, NetShow Theater Server configures them all as low-performance disks. For example, if you have three 9-GB capacity hard disk drives capable of a 5-Mbps transfer rate, and one 1.5-GB capacity hard disk drive capable of a 3-Mbps transfer rate, NetShow Theater Server Setup configures them all equally to perform as 1.5- GB capacity hard disk drives capable of a 3-Mbps transfer rate.

CAUSE
When Setup measures system drive performance, it reads or writes data at every drives' maximum I/O capabilities. This can cause saturation of the SCSI controller or PCI bus. On systems with many fixed disk drives and/or PCI drive controllers, Setup may report extremely low streams per disk, either significantly lower than the drives performance rating or certain specific drives may have much lower ratings than one or two identical drives on the same bus.

It is possible to saturate a PCI bus with 6 ultra wide SCSI chains supporting a total of 23 drives. Setup may report that one or two drives have high ratings (12 streams/disk), but the other drives have lower ratings (0 to 4 streams/disk). When Setup runs using fewer drives, the aggregate drive bandwidth remains the same, indicating that the drive performance is limited by a SCSI bus/controller and/or PCI bus saturation, and not the I/O performance of the drives themselves.

WORKAROUND
To work around this problem, use one of the following resolutions:

Balance the system by moving some of the drives over to another PCI bus, reducing the disk drive I/O load on any one bus.

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Do not run in Ultra mode. With four SCSI channels on one PCI bus, you are still saturating the PCI bus while the controllers are set to run in Ultra Wide mode. After you set the controllers to run in non-Ultra mode, the system drive performance reports should improve.

MORE INFORMATION
Please note that you can run NetShow Theater Server Setup to test your hardware and find out the actual number of concurrent streams per disk without completing Setup and installing any NetShow Theater Server components.

There are multiple variables that can affect the maximum stream count available from a Theater Server installation. In the example above, we are using a system that is content drive I/O limited only and not limited by other possible factors such as, network interface card performance, physical network limitations, use of Theater Server Fault Tolerance, and bit rate of the MPEG media.

Specific details on these other stream count limiting variables can be found in the online NetShow Theater Server documentation file NetShowTS.chm, located in the NetShow Theater\Docs\HTML directory of your NetShow Theater Server media. Search on keywords such as bus, SCSI, performance, fault tolerance, and bit rate.

The NetShow Theater Server Web site http://www.microsoft.com/theater/ also provides an online Capacity Planner that provides the ability to play out scenarios with the variance of most of these limiting variables.

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