Intel AS/400 RISC Server, 170 Servers, 7xx Servers manual Native vs. Virtual Performance

14.6.2.1 Native vs. Virtual Performance

Figure 1 shows a comparison of measured bandwidth using virtual SCSI and local attached DASD for reads with varying block sizes of operations. The difference in the reads between virtual I/O and native I/O in these tests is attributable to the increased latency using virtual I/O. The difference in writes is caused by misalignment, which causes a read for every write. A write alignment change is planned for a future IBM i operating system release which will make virtual and native writes similar in speed.

Native vs. Virtual

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Figure 1 - The figure above shows a comparison of native vs virtual. This experiment shows that virtual write performance is significantly less then native. Read performance performs similar or better then native depending on the read-cache performance.

14.6.2.2 Virtual SCSI Bandwidth-Multiple Network Storage Spaces

Figure 2 shows a comparison of measured bandwidth while scaling network storage spaces with varying block sizes of operations. The difference in the scaling of these tests is attributable to the performance gain, which can be achieved by adding multiple network storage spaces. This experiment shows that in order to achieve better performance from the hard disk, multiple network storage spaces can be used.

15Disk 5GB Sequential Read

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15 Disk 5GB Sequential Write

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1 NWSS		2 NWSS		4 NWSS		8 NWSS

Figure 2- The figures above show performance while scaling network storage spaces. This experiment shows that adding NWSS increases the throughput for read/write performance. The best performance is achieved by using 8 NWSS.

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008	Chapter 14 DASD Performance	235