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High Queue Depth Sequential Performance

OCZ RevoDrive Hybrid: Solid-State Speed With Hard Drive Capacity
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Application-level testing represents the performance you would see from these five configurations in everyday desktop use. But it doesn't really help us determine if OCZ's write-back caching strategy is any better than the write-through default Intel recommends for Smart Response Technology.

This drive needs to live up to its RevoDrive namesake, which is why we're turning to ATTO and maxing out queue depth. If you're shopping for a PCI Express-based SSD, it's because you need the sort of throughput not available from a conventional 6 Gb/s SATA drive, and you have the workloads able to push data rates that high with a number of outstanding requests.  

Bear in mind that the graph above applies to data living on the RevoDrive Hybrid's flash. Because ATTO tops out at 2 GB of LBA space, it operates completely within this drive's NAND memory. Naturally, that's only representative of a best-case scenario, where you're reading information that has already been cached.

In such an environment, the benefits of the RevoDrive Hybrid are clear, and OCZ's mixed-media offering delivers performance similar to what you'd get from a RevoDrive 3. In sequential reads, it's actually possible to achieve more than 1 GB/s if you're moving large bits of data at high queue depths. Sequential writes aren't as impressive. But again, so long as you're operating exclusively on data within that 100 GB cache, you're going to realize great performance, outpacing any other caching solution.

So, what happens when you start reading or writing data that isn't already cached? After all, this product boasts 1 TB of capacity, only one-tenth of which fits in flash. Once you fill that space and have to start ejecting data from the cache and writing it to disk, performance drops off precipitously.

In an attempt to demonstrate what happens, we turn to Iometer and set an LBA range of 200 GB. There, sequential writes are seen to drop as low as 55 MB/s. That's the less-glamorous figure we come up with when information must be evicted from cache and then written to disk.

How about when you need to read data on the hard drive, before it's actually cached? Iometer logs indicate that Toshiba's 5400 RPM drive gives you something closer to 70-80 MB/s. Obviously, that's hardly ideal. But it's what you have to expect before data is cached.

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