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The Benefit of Hybrid Drives

Between Worlds

Article from ADMIN 22/2014

By Jens-Christoph Brendel

People still use hard disks even when SSDs are much faster and more robust. One reason is the price; another is the lower capacity of flash storage. Hybrid drives promise to be as fast as SSDs while offering as much capacity as hard drives. But can they keep that promise?

The question of whether hybrid drives are worthwhile is not as easy to answer as it seems at first glance. If you were to measure their performance with a conventional synthetic benchmark, you would in most cases be unable to determine any difference from an ordinary hard drive (Figure 1, first run). This is because they try to fill their relatively small (and therefore cheap) flash memory with the data that is used most frequently. For this much-used data, subsequent access no longer needs to rely on the comparatively slow rotating disks of the hard drive, because the data instead comes from the integrated multilevel cell (MLC) flash memory module.

However, the algorithm of the hybrid drive can only identify frequently used data because they have been read or written multiple times in a given period. A benchmark that generates new random data for each run, and then reads them once only, is always served by the traditional hard disk and never has a chance to accommodate its reading material on the fast SSD.

However, you can sometimes store the test data for multiple use and re-use in a file (e.g., the fio workload simulator). Additionally, practically oriented application benchmarks are more likely to help: One example is Windows PCMark Vantage. In terms of hard drives, this benchmark tests gaming and streaming, adding music and images to a media library or application, and system startup, among other things. Various published values that clearly show the superiority of the hybrid drives can also be achieved here if you run the benchmark several times consecutively and without interruption by other applications; this is the only way to fill the cache with the correct data (Figure 1).

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