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  Oracle Tips by Burleson

SSD Results

The SSD results using the RamSan400 were anything but typical. Remember that the RAC systems tested were identical down to the host bus adapter (HBA). The only variable was whether the RAID or SSD system was used.

SSD Throughput

As with the RAID system, the transactions per second (TPS) will be examined as the amount of server memory is decreased. This drives I/O to the RamSan-400. Figure 4.8 shows the results from this decrease in server cache memory.

As I/O is forced to the RamSan-400, the TPS actually increases. This is because the I/O speed of the RamSan-400 is actually much better than the latency of the RAC high-speed interconnect. The interconnect speed is the primary driving factor in the fully cached system as the transactions are limited by the amount of data that must be transferred and the latency of the interconnect. With the non-fully cached server the number of transactions is dependent more upon the speed of the underlying I/O subsystem. Hence, when a system exists with I/O speed that is faster than the interconnect latency, the TPS is increased by driving I/O away from the interconnect and to the I/O subsystem!

SSD Bytes per Second

What about bytes per second? Figure 4.9 shows the results from decreasing the per-instance server memory for a RamSan-400 based system. As the memory in the server that was allocated to Oracle was decreased by resetting the sga_max_size and sga_targetsettings in the SSD based test, bytes per second increased. Figure 4.9 shows the results on total bytes per second from decreasing the per-instance memory for a RamSan-400 based system.

This figure shows how the bytes-per-second increases as dependency on the interconnect is removed and the system moves away from being fully cached when using SSD technology. This is due to the factor of ten or more difference between the average latencies of the cluster interconnect and the speed of reads and writes on the SSD system.

SSD Average Transaction Time

Perhaps the most dramatic difference is in the average transaction time results when comparing the RAID to the SSD system. As expected from a review of the previous SSD results, a decrease in the average transaction time should be expected allowing more transactions and more bytes per second. However, a very dramatic decrease as cache memory was reduced was seen. Look at Figure 4.10.

Once dependence on the interconnect is mitigated, the transaction times dramatically improved by several orders of magnitude. The scale on the graph in Figure 4.10 is logarithmic. This means that for one increase in scale on the vertical axis, an increase by a factor of 10 can be seen. Compare the average transaction times in Figure 4.10 to those from the RAID tests in Figure 4.6. The dramatic difference between the two technologies can be seen as memory is reduced. This indicates that by utilizing the RamSan400 SSD system transaction times were improved by nearly a factor of 100, two orders of magnitude!

SSD Average Response Times

Since the average response time is dependent on transaction times, the results for the RamSan400 mirror those for average transaction time is shown in Figure 4.11.

Again note the logarithmic vertical scale. As with average transaction time, a nearly 2 order of magnitude difference can be seen when the latency of the RAC high-speed interconnect is mitigated as a factor in response time. Comparing the RAID average response time in Figure 4.7 to SSD average response time in Figure 4.11 also highlights the dramatic difference between the two storage subsystems.

The above book excerpt is from:

Oracle RAC & Tuning with Solid State Disk

Expert Secrets for High Performance Clustered Grid Computing

ISBN 0-9761573-5-7

Donald K. Burleson & Mike Ault


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