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Samsung 850 Pro 256GB Three-Drive SSD RAID Report

By: Jon Coulter | RAID in Storage | Posted: Jan 9, 2015 3:14 pm

Futuremark PCMark 8 Extended - Consistency Test


Heavy Usage Model


We consider PCMark 8's consistency test to be our heavy usage model test. This is the usage model most enthusiasts, heavy duty gamers, and professionals fall into. If you do a lot of gaming, audio/video processing, rendering, or have workloads of this nature, then 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 the 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 an average of 13 to 17 hours to complete, and it writes somewhere between 450GB and 14,000GB of test data, depending on the drive/array being tested. If you want to know what a 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 ten minutes.

2. Run performance test (one pass only).

3. Repeat one and two, eight times, and on each pass, increase the duration of random writes by five 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 one and two, five times.


Recovery phase:


1. Idle for five minutes.

2. Run performance test (one pass only).

3. Repeat one and two, five times.



Storage Bandwidth


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




We consider steady state bandwidth (the blue bar) to be our test that carries the most weight in ranking a drive/array'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 orange and red bars) is what we consider the second most important aspect when ranking a drive/array's performance. Trace based consistency testing is where true high performing SSDs are separated from the rest of the pack.


Even though our 850 Pro array was able to dominate our synthetic testing by easily winning every test, quite the opposite occurred when we moved to real-world simulations. In this, our most important test, our 850 Pro array was unable to keep pace with our top arrays.


We have seen this before, so it's not really much of a surprise. Granted, this result is better than all but one consumer based PCIe SSD (Samsung's XP941 m.2 drive) running on the AHCI protocol, but in the end, it's somewhat disappointing. The 850 Pro in RAID 0 does not like the incompressible mixed random workloads that this testing simulates, and that's our measure of true performance.


We were hoping to see a new RAID champion crowned today, but that's just not in the cards for the 850 Pro.




We chart our test subject's storage bandwidth as reported at each of the test's 18 trace iterations. This gives us a good visual perspective of how our test subjects perform as testing progresses.



Total Access Time (Latency)


We chart the total time the disk is accessed as reported at each of the test's 18 trace iterations.





Disk Busy Time


Disk Busy Time is how long the disk is busy working. We chart the total time the disk is working as reported at each of the tests 18 trace iterations.




When latency is low, disk busy time is low as well.



Data Written


We measure the total amount of random data that the drive/arrays are capable of writing during the degradation phases of the consistency test. The total combined time that degradation data is written to the drive/array is 470 minutes. This can be very telling. The better the drive/array can process a continuous stream of random data, the more data will be written.




Workload latency is a problem for the 850 Pro in RAID 0, and this chart serves to illustrate that point.


Gratuitous Benchmarking


This is where we show you what our array's performance looks like when powered by the fastest operating system for SATA based storage ever made, Windows Server 2008. This is the exact same hardware, just an OS change.










Massive synthetic performance is exhibited with nearly 900MB/s 4K QD1 write performance in CDM, which is definitely a lab record.


You can't get performance like this from Windows 8 or 8.1; you can get very close with Windows 7, or Server 2012, but nothing performs quite as well as Server 2008 when it comes to SATA based storage. 4K write performance is vastly superior on Server 2008 and Windows 7 in comparison to Windows 8 or 8.1.

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