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Benchmark Results: Boot-Up In hIOmon

In The Lab With Seagate's Momentus XT 750 GB Hybrid HDD
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Based on the preceding page's ASU benchmarks, Seagate's Momentus XT looks a lot more promising. But let’s first consider how synthetics translate to the real-world before getting too ahead of ourselves.

For this, we're using hIOmon, a file and disk I/O performance measuring tool that can concurrently monitor I/O operation activity within three distinct levels of the software and hardware stack: namely, the logical disk level (the file system), the physical volume level, and the physical device level. The image below helps visualize each level of the stack, and it comes from a SNIA webcast that discusses the complexities of how I/Os traverse the stack. You can find that webcast here.

Monitoring results from the logical disk level are obtained between the operating system I/O manager and the file system. Results from the physical volume level are gleaned between the file system and the volume manager, and results from the physical device come from in between the volume manager and the disk class driver.

The difference in I/O activity between the logical disk level and the physical disk can vary significantly. In the graphs below, we capture data from the latter portion of the boot-up process. Booting up consists of a number of stages, starting with a power-on self-test, proceeding on to the BIOS ROM and boot loader phase, and then the firing-up of various configured services and other start-up tasks.

hIOmon is normally configured to begin monitoring once the services start to load (hIOmon can optionally be configured to begin monitoring earlier in the process). Due to the dynamic nature of the boot process, the measurements taken can vary significantly from run to run, which is evident from our results below. The largest variation occurs at the logical disk level.

Although the difference in the amount of data transferred is quite significant, it does not (in this case) have a significant impact on the percentage of fast IOPS or the average block transfer size. To clarify, a fast I/O is an operation observed by hIOmon to have completed in less than one millisecond.

The boot-up processes that we monitored typically consist of approximately 88% random read access and 12% sequential read access, with an average queue depth of 1.4.

If there's one key take-away, it's that a significant amount of I/O activity can occur independent of the storage device, which significantly reduces demands made on the storage system. As a result, the potentially poor performance of a storage solution can be masked to a degree. This is evident in the increased percentage of fast IOPS and the higher maximum transfer rate achieved at the logical disk level when we monitor Western Digital's Raptor X.

When we monitor the Momentus XT's boot-up process, we see that performance increases at both the logical disk and physical device level for both the percentage of fast IOPS and the maximum transfer rate.

On Samsung's 830, the percentage of fast IOPS is identical at both the logical disk and physical device levels. Meanwhile, the maximum transfer rate increases at each level.

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