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Crucial M550 512GB 2-Drive SSD RAID Report

By: Jon Coulter | RAID in Storage | Posted: May 28, 2014 2:50 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 on average 13 to 17 hours to complete, and it writes somewhere between 450GB and 8000GB of test data, depending on the drive(s) 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 blue bar) 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 orange and red bars) 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.


A single M550 does not have compelling steady state performance, but our 2-drive array certainly does. Notice how a single M550 manages only 124 MB/s storage bandwidth in a steady state. The steady state performance of our 2-drive M550 array is well over double that of a single M550. This is what we mean by scaling; this is why a SATA based array delivers superior performance in an OS environment.


We retired our 840 Pro array from this testing due to its inferior performance. In its place, I thought it would be interesting to see how a PCIe SSD would fair against our top arrays. Comay's BladeDrive 480GB PCIe SSD has an advertised sequential read/write speed of 2000 MB/s. Sequential performance is nice for secondary attached storage, but in an OS disk environment, random 4k performance reigns supreme. The BladeDrive is no match for any of our arrays in an OS environment. I am of the opinion that until PCIe is RAID capable, it's not going to provide compelling OS disk performance.




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)


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




The M550 has higher latency than the rest of the drives on our chart in a steady state. As soon as our M550 array gets a break, TRIM does its job, and our M550 array finishes with the lowest latency of any array on our chart.



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. Our M550 array is able to spend up to 3.5 times less time working than a single M550.



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 drives is 470 minutes. This can be very telling. The better the drives can process a continuous stream of random data, the more data will be written.




Our M550 array is able to write 1500 gigabytes of random data in 470 minutes. The M550's lack of overprovisioning and consumer pedigree conspire to deliver weak performance in this test. Drives like the 600 Pro and the 730K have enterprise DNA, and they are able to write continuous streams of random data many times faster than drives with consumer DNA. The ComayBlade is supposed to be a drive designed for enterprise class performance, yet it delivers very poor random write performance.

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