When designing a san for performance it means firstly

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When designing a SAN for performance, it means firstly having to determine the performance requirements, and the application I/O profile. Even if the SAN is already in production, you need to understand the application profile to determine how you can optimize or maintain performance. Without this knowledge, any change or upgrade could result in a lowering of performance. Availability is also another consideration. But be aware that designing or redesigning a SAN for availability will probably change the performance characteristics of the SAN.
Accelerated SAN Essentials 14 -4 © 2010 Hewlett-Packard Development Company, L.P. UC434S F.00 Performance factors Performance factors Attenuation Bandwidth Data rate Applied load Request size Read/write ratio Request rate •ResponseTime •Rotational Speed •Seek Time •Service Time •Throughput •Utilization •Bus Contention Complicating the task of delivering good performance is the lack of meaningful performance measurement standards. Although vendors and analysts often cite benchmarks such as high rates of I/O and cache hits or low seek times on disk drives as examples of good performance, these statistics offer little insight to SAN design. A number of factors contribute to the difficulties an administrator has in gathering and interpreting accurate performance data. The biggest issue is the collection of performance statistics. This data may be spread across every component in the SAN — the database, the operating system, the host bus adapter (HBA), the switch, and the storage array. SAN administrators need to verify that they have gathered all of the data required before beginning analysis. It is imperative to make sure the clocks of the components being measured are all synchronized. A few minutes difference, or even a few seconds, on any of the internal time clocks in the components could distort the interpretation of the results. There are many tools available on the market that measure performance in a SAN. However, performance-tuning software can create a new set of performance problems by slowing down the SAN.
Performance UC434S F.00 © 2010 Hewlett-Packard Development Company, L.P. 14 -5 Performance terms The following definitions are frequently used to describe performance: Attenuation - Loss of power specified in decibels per kilometer (dB/km). Bandwidth – total amount of data transferred through a medium or system per unit of time. Raw Bandwidth – line speed – Theoretical rate of a component, a transmission line or bus has a physical signal rate that determines the maximum possible data rate. Sustained Bandwidth – Is the data rate after accounting for all the overheads that might be needed for the transmission operations. Sustained bandwidth will always be less than the Raw Bandwidth if the transmission medium has contention or if parts of the transmission are not considered to be useable data.

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