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Results: TRIM Testing

The Crucial M550 SSD Review: Striking Back With More Performance
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Finally, I want to introduce a new test I've been working on using JEDEC's 218A consumer workload trace to create a TRIM benchmark. It's not a neatly-packaged little utility you can run at home. Rather, this is a test scripted in ULINK's DriveMaster 2012 software and hardware suite.

DriveMaster is used by most SSD manufacturers to create and perform specific metrics. It's currently the only commercial product that can create the scenarios needed to validate TCG Opal 2.0 security, but it's almost unlimited in potential applications. There are various hardware components associated with the platform, such as a SATA/SAS power hub that allows the benchmarked drive to be power-cycled independently of the platform. Much of the benefit tied to a solution like DriveMaster is its ability to diagnose bugs, ensure compatibility, and issue low-level commands. In short, it's very handy for the companies actually building SSDs. And if off-the-shelf scripts don't do it for you, make your own. There's a steep learning curve, but the C-like environment and command documentation gives you a fighting chance.

This product also gives us some new ways to explore performance. Testing the TRIM command is just the first example of how we'll be using ULINK's contribution to the Tom's Hardware benchmark suite.

The suite ships with some built-in scripts, but also contains its own scripting language for extensibility and customization. This particular test uses JEDEC's published master trace of consumer I/O activity (similar to our Tom's Hardware Storage Bench trace). The read commands are removed from the trace, leaving write, flush, and TRIM commands. After secure erasure and writing preparatory data, the test commences. The trace is played against the drive four times using NCQ with and without TRIM, and DMA with and without TRIM. IOPS are measured and averaged every 100,000 commands. 

On a 256 GB drive, each iteration writes close to 800 GB of data, so running the JEDEC TRIM test suite once on a 256 GB SSD generates almost 3.2 TB of mostly random writes (it's 75% random and 25% sequential). By the end of each run, over 37 million write commands are issued. If that sounds like a lot of storage traffic, it is.

The first two tests employ DMA to access the storage, while the last two use Native Command Queuing. Since most folks don't use DMA with SSDs (aside from some legacy or industrial applications) we don't concern ourselves with those. It can take up to 96 hours to run one drive through all four runs, though faster drives can cut the time in half, roughly. Because so much information is being written to an already-full SSD (the drive is filled before each test, and then close to 800 GB are written per iteration), SSDs that perform better under heavy load fare best. Without TRIM, on-the-fly garbage collection becomes a big contributor to high IOPS. With TRIM, 13% of space gets TRIM'ed, leaving more room for the controller to use for maintenance operations.

TRIM Testing

Here's the chart derived from our DriveMaster JEDEC TRIM test data. We have the new M550s, Samsung's venerable 840 Pro at 256 GB, Crucial's more mainstream M500 (240 GB), Plextor's M5P, and the 250 GB 840 EVO. Each device's NCQ-based test is plotted. The solid line represents average IOPS every 100,000 commands, but without TRIM. The hashed line represents performance every 100,000 commands with TRIM. In each case, the workload is mixed in with tons of small, random writes.

Since performance is measured over each 100,000-command segment, time is factored out of the above chart. This rolling average also hides the trace's peaky nature.

You can see the 512 GB M550 start out with lower peak performance in non-TRIM testing. Add TRIM to the mix, though, and it ends up as quick as Samsung's 840 Pro.

But I also want the instantaneous average of our TRIM testing. So, how does the drive fare servicing writes with and without TRIM during each 100,000-command window? The purple line represents IOPS across the entire trace, without TRIM. The teal line is with TRIM.

Notice that the peaks are higher with TRIM support enabled. This is how a desktop-oriented drive should behave. About 13% of the drive's span is freed by the command during our test, giving Marvell's controller more available blocks to write to. Without TRIM, the processor is stuck manually collecting garbage, juggling data in read/modify/erase cycles.

TRIM mitigates this, allowing the operating system to tell the drive when a range of LBAs is no longer needed. The alternative is letting the drive handle its own garbage collection as the operating system writes to LBAs already occupied by data.

This chart shows throughput in our TRIM-enabled test. The M550s do well, despite their lack of additional over-provisioning. See how soundly the 512 GB M550 routs the 480 GB M500?

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