Oracle Database Appliance: Storage Performance — Part 1
Today I want to show what kind of IO performance we can get from Oracle Database Appliance (ODA). In this part, I will focus on hard disks. That’s right — those good old brown spinning disks.
I often use Oracle ORION tool to stress-test an IO subsystem and find it’s limits. It’s a very simple and handy tool and usually provide most of the IO simulation I need.
I usually benchmark for small random IOs and for large sequential reads. This gives me a good idea what I can expect from this IO subsystem for OLTP workloads as well as bulk data processing workloads including data warehousing, backups and batch activity. I usually don’t stress test mixed workload until I know what’s the profile of the application that I will run on this platform. In this particular case, I’m more after generic IO stress test and finding the limit.
Today, let’s talk about small random IOs which is the attribute of the OLTP workloads. I’m interested in single IO response time and IOs per second (IOPS).
When I stress test an IO subsystem I usually process average numbers but I always remember that averages are just that — averages. Because my artificial ORION workload is pretty randomly distributed and I use reasonably small intervals, the results have good confidence for me but in some cases I would want to dig further and collect some histograms of IO latencies. I haven’t done it for Oracle Database Appliance though and knowing what’s behind I expect response time to be quite consistent – there is no disk cache or something similar that skews response time.
I should note that I use term IO response time and IO latency interchangeable here in case you are using these terms differently. It might be a bad habit but that’s what I do.
Before I stress test an IO subsystem, I usually set some expectations. Let’s do the same here. ODA has 20 disks – 15K RPM SAS disks. My experience tells me that I should expect very good single IO latency (below 10ms) from these disks serving at least 100 IOPS each. I also expect that these disks will still provide reasonable response time if you crank up the workload to about 200 IOPS but this is where I would see much higher response times — getting into 20ms range. Now, I know that 15K RPM SAS disk can deliver even more IOPS each but then IO response time becomes generally unacceptable for OLTP systems. In fact, 10 ms target is what’s been a good rule of thumb in the last decade.
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