Performance Consistency

Performance consistency tells us a lot about the architecture of these SSDs and how they handle internal defragmentation. The reason we don’t have consistent IO latency with SSD is because inevitably all controllers have to do some amount of defragmentation or garbage collection in order to continue operating at high speeds. When and how an SSD decides to run its defrag or cleanup routines directly impacts the user experience as inconsistent performance results in application slowdowns.

To test IO consistency, we fill a secure erased SSD with sequential data to ensure that all user accessible LBAs have data associated with them. Next we kick off a 4KB random write workload across all LBAs at a queue depth of 32 using incompressible data. The test is run for just over half an hour and we record instantaneous IOPS every second.

We are also testing drives with added over-provisioning by limiting the LBA range. This gives us a look into the drive’s behavior with varying levels of empty space, which is frankly a more realistic approach for client workloads.

Each of the three graphs has its own purpose. The first one is of the whole duration of the test in log scale. The second and third one zoom into the beginning of steady-state operation (t=1400s) but on different scales: the second one uses log scale for easy comparison whereas the third one uses linear scale for better visualization of differences between drives. Click the buttons below each graph to switch the source data.

For more detailed description of the test and why performance consistency matters, read our original Intel SSD DC S3700 article.

  Samsung SSD 850 Pro Samsung SSD 840 Pro SanDisk Extreme Pro Intel SSD 730 OCZ Vector 150
7% Over-Provisioning - - -
12% Over-Provisioning
25% Over-Provisioning

Wow, this is awesome. Even with the default 7% over-provisioning, the 850 Pro is pushing almost as many IOPS as the Extreme Pro with its 12% over-provisioning. When the over-provisioning is increased to the same 12% level, the 850 Pro is a leader without a doubt. Only the Vector 150 can come close, although it is nowhere hear as constant as the IOPS is ranging between 10K and 30K, whereas the 850 Pro can maintain a steady line.

When compared with the 840 Pro, the upgrade is tremendous. IO consistency was always the weak point of the 840 Pro, so it is great to see that Samsung has paid a great effort to fix that in the 850 Pro. A part of the performance increase obviously comes from the usage of V-NAND because with shorter program and erase latencies, the steady-state performance increases as the garbage collection takes less time and there are more empty blocks available.

Some of you may wonder the odd capacities at 25% over-provisioning but the reason is that I noticed an error in the old ones. Basically, the old 25% numbers were in gibibytes (i.e. 1024^3 bytes) whereas the other capacities have always been in gigabytes (1000^3 bytes). I decided to unify the capacities and now they are all reported in gigabytes. The actual testing or over-provisioning levels have not changes -- it is simply a matter of how the capacities are represented.

  Samsung SSD 850 Pro Samsung SSD 840 Pro SanDisk Extreme Pro Intel SSD 730 OCZ Vector 150
7% Over-Provisioning - - -
12% Over-Provisioning
25% Over-Provisioning

 

  Samsung SSD 850 Pro Samsung SSD 840 Pro SanDisk Extreme Pro Intel SSD 730 OCZ Vector 150
7% Over-Provisioning - - -
12% Over-Provisioning
25% Over-Provisioning

 

RAPID 2.0: Support For More RAM & Updated Caching Algorithm AnandTech Storage Bench 2013
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  • Homeles - Monday, June 30, 2014 - link

    Man, the 850 Pro is killer. Samsung really knocked it out of the park. Those prices are just completely out of touch, though. Reply
  • Awful - Monday, June 30, 2014 - link

    Yeah the prices are high for now. Game changing stuff though; and prices can only come down. PCIe V-NAND? Yes please! Reply
  • Hung_Low - Tuesday, July 01, 2014 - link

    Even better, Intel style NVMe controller + this v-nand!! orgasmic Reply
  • avyshue - Tuesday, July 01, 2014 - link

    yeah, i've been holding off on upgrading from my existing 128 boot drive + mechanical setup to a full 1TB drive. I think I'll keep holding out until PCIe is better supported/better priced. Reply
  • Angrychair - Tuesday, July 01, 2014 - link

    The prices are in line for class leading performance and reliability.

    The reliability is the critical part, these are drives that are unlikely to wear out in any system almost no matter how heavily taxed.
    Reply
  • Ken_g6 - Tuesday, July 01, 2014 - link

    I see these are MLC drives. Hopefully, Samsung will come out with consumer-level 3D TLC drives that have relatively good reliability, and a price at or below Crucial's drives. Reply
  • frenchy_2001 - Tuesday, July 01, 2014 - link

    Reliability is a side effect of retreating to 40nm pitch technology.
    Even if they decided to do TLC with the same cells, they would probably end up being more reliable than 2D nand MLC.
    Reply
  • joelypolly - Thursday, July 03, 2014 - link

    They already have drives in testing that has written over 8 petabytes so I think the reliability is there Reply
  • mkozakewich - Saturday, July 05, 2014 - link

    On that note, I'm wondering how 4-bit MLC would perform compared to 2D NAND. Reply
  • RaistlinZ - Monday, June 30, 2014 - link

    Fantastic drives! That consistency is really remarkable. I don't know if most will pay the price premium for these over the EVO however. The average user probably wouldn't notice a difference in general day to day use. Reply

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