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SanDisk Extreme II 240GB 6-Drive SSD RAID Report

By: Jon Coulter | RAID in Storage | Posted: Apr 1, 2014 2:00 pm

Futuremark PCMark 8 Extended - Consistency Test


Heavy Usage Model:


We consider PCMark 8's consistency test our heavy usage model test. This is the usage model most enthusiasts, gamers, and professionals fall into. If you do a lot of gaming, audio/video processing, rendering, or have workloads of this nature, this test will be most relevant to you.


PCMark 8 has built-in, command-line-executed storage testing. The PCMark 8 Consistency test measures the performance consistency and degradation tendency of a storage system.


The Storage test workloads are repeated. Between each repetition, the storage system is bombarded with a usage that causes degraded drive performance. In the first part of the test, the cycle continues until a steady degraded level of performance has been reached (Steady State).


In the second part, the recovery of the system is tested by allowing the system to idle and measuring the performance with long intervals (TRIM).


The test reports the performance level at the start, the degraded steady-state, and the recovered state, as well as the number of iterations required to reach the degraded state and the recovered state.


We feel Futuremark's Consistency Test is the best test ever devised to show the true performance of solid state storage in a heavy usage scenario. This test takes on average 13 to 17 hours to complete and writes somewhere between 450GB and 7000GB of test data depending on the drives being tested. If you want to know what an SSD's performance is going to look like after a few months or years of heavy usage, this test will show you.


Here's a breakdown of Futuremark's Consistency Test:


Precondition phase:

1. Write to the drive sequentially through up to the reported capacity with random data.

2. Write the drive through a second time (to take care of overprovisioning).


Degradation phase:

1. Run writes of random size between 8*512 and 2048*512 bytes on random offsets for 10 minutes.

2. Run performance test (one pass only).

3. Repeat 1 and 2 for 8 times, and on each pass increase the duration of random writes by 5 minutes.


Steady state phase:

1. Run writes of random size between 8*512 and 2048*512 bytes on random offsets for 50 minutes.

2. Run performance test (one pass only).

3. Repeat 1 and 2 for 5 times.


Recovery phase:

1. Idle for 5 minutes.

2. Run performance test (one pass only).

3. Repeat 1 and 2 for 5 times.


Storage Bandwidth


PCMark 8's Consistency test provides a ton of data output that we can use to judge a drive's performance.




We consider steady state bandwidth (the orange bar) as our test that carries the most weight in ranking a drive's performance. The reason we consider steady state performance more important than TRIM is that when you are running a heavy duty workload, TRIM will not be occurring while that workload is being executed. TRIM performance (the blue bar) is what we consider the second most important consideration when ranking a drive's performance. Trace-based consistency testing is where true high performing SSDs are separated from the rest of the pack. Take a good look at how even a single Extreme II defeats a two-drive 840 Pro array. The 840 Pro is what I call a "Benchmark Babe" because it wins all the benchmarks that don't matter. Notice the performance drop off from TRIM to Steady State. Notice that the more the drives are over provisioned the less performance drops. The Extreme II's performance drop from TRIM to Steady State is relatively small in comparison to the Q Series Pro because the Extreme II is over provisioned 7 percent and the Q Series Pro isn't over provisioned.


As you can see, SanDisk's Extreme II is a performance powerhouse. The Extreme II is efficient; it is so efficient that TRIM doesn't even matter a whole lot. No matter what you do to an Extreme II, that SanDisk magic is going to deliver performance that's class leading. This is the test I use to determine our RAID performance champion and my personal single drive champion. The Extreme II wins on both fronts by delivering superior performance in a Steady State and becomes TweakTown's new performance leader.


Disk Busy Time


Disk Busy Time is how long the disk is busy working. We measure the total time the disk is busy while replaying all 18 trace iterations.






The Extreme II is incredibly efficient. Our Extreme II array spends very little time working. Contrast that to the 840 Pro array that struggles over four times longer. This is another way we see overprovisioning at work. Notice how the Extreme II spends less time working than the Q Series Pro even though they are pretty much equally matched.


Total Access Time


Access time is the time delay or latency between a request to an electronic system and the access being completed or the requested data returned. Access time is how long it takes to get data back from the disk. We measure the total time the disk is being accessed while replaying all 18 trace iterations.






This is our clearest example of the benefits of RAID write caching. Notice how much better access performance is when utilizing an array in comparison to a single drive. Access times are close to 3.5 times better for a two-drive Extreme II array in comparison to a single Extreme II. This isn't a function of scaling; this is a function of write caching, caching that's not available for a single drive.


Data Written


We measure the total amount of random data that the drives are capable of writing during the degradation phases of the consistency test. The total combined time that degradation data is written to the drive is 220 minutes. This can be very telling. The better the drive can process a continuous stream of random data, the more data will be written.




In my opinion, nothing I've ever seen more clearly shows the benefit of over-provisioning than this chart does. Notice how our Extreme II array is capable of writing more random data than our Q Series Pro array in the same amount of time. This is because the Extreme II is overprovisioned and the Q Series Pro is not. Now, compare that to the heavily overprovisioned 600 Pro array. The more overprovisioning a drive has, the better it will perform the heaviest of workloads. This is a metric that, until now, has been hard to quantify because it won't manifest itself in a meaningful way except in certain scenarios like this one.

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