Inside The Drives

There are three different PCB designs in the 850 EVO lineup. The 120GB and 250GB models (above) use a tiny PCB with room for two NAND packages (one on each side). Interestingly enough, both use octal-die packages, meaning that the 120GB 850 EVO only has a single 128GB (8*16GB) NAND package. Decoding the part number reveals that the packages are equipped with eight chip enablers (CEs), so a single NAND package is viable since all eight dies can be accessed simultaneously.

The use of octal-die packages is actually true for all capacities. It's an interesting choice nevertheless, but I suspect Samsung's packaging technology is advanced and mature enough that it's more cost efficient to use high die count packages and small PCBs instead of larger PCBs with more and less dense NAND packages.

Samsung SSD 850 EVO NAND Configurations
Capacity 120GB 250GB 500GB 1TB
# of NAND Packages 1 2 4 8
# of Die Per Package 8 8 8 8
Total # of Die 8 16 32 64
Die Capacity 128Gbit 128Gbit 128Gbit 128Gbit
Raw NAND Capacity 128GiB 256GiB 512GiB 1024GiB
Over-Provisioning 12.7% 9.1% 9.1% 9.1%

TurboWrite

TurboWrite is a feature that Samsung brought to the 840 EVO to increase write performance. The idea of running a small portion of the NAND in SLC mode was nothing new, but it was the first time it truly made sense because the 840 EVO used slower TLC NAND and hence the SLC buffer could provide significant improvements to write performance and user experience. Unsurprisingly, TurboWrite is also present in the 850 EVO.

Samsung SSD 850 EVO TurboWrite SLC Buffer Size
Capacity 120GB 250GB 500GB 1TB
TurboWrite Buffer Size 3GB 3GB 6GB 12GB

The buffer sizes and core architecture have remained unchanged. All writes hit the SLC buffer first, from which they then get moved to the TLC array during idle time. The only exception is a case of long, sustained period of writes that exceeds the buffer size, in which case the data will be written straight to the TLC portion.

Write Performance With and Without TurboWrite
  With TurboWrite Without TurboWrite
  Sequential Write 4KB Random Write (QD32) Sequential Write 4KB Random Write (QD32)
120GB 520MB/s 88K IOPS 150MB/s 38K IOPS
250GB 520MB/s 88K IOPS 300MB/s 70K IOPS
500GB 520MB/s 90K IOPS 500MB/s 80K IOPS
1TB 520MB/s 90K IOPS 520MB/s 80K IOPS

Samsung's reviewer's guide states that the 850 EVO features "enhanced TurboWrite technology" with a focus on random write performance, but I don't have any additional details as to how the TurboWrite implementation in the 850 EVO differs from the 840 EVO. TurboWrite was always designed to cache all writes regardless of the nature of the write (random vs sequential), so I'm not sure if anything has actually changed. Obviously the algorithms have been optimized for the new NAND and controller architecture and it's possible that the whole batch of algorithms has improved in the process, but I'll provide an update when I hear back from Samsung.

I ran a quick sequential write test to see how TurboWrite behaves in the 850 EVO. At smaller capacities it clearly provides a tremendous performance boost, but at 500GB and 1TB there is enough NAND to provide the parallelism that is needed to max out the SATA 6Gbps interface. That is a big improvement over the 840 EVO as its write performance maxed out at ~400MB/s when writing to the TLC array, so the performance benefits of 3D NAND technology are already evident.

Introduction, The Drives & The Test Three Bits and Three Dimensions: What's the Deal?
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  • TEAMSWITCHER - Monday, December 08, 2014 - link

    I'm in complete agreement. I'm not going to buy another 2.5" SSD before I can get an 850 Pro (512 GB) equivalent with an M.2 interface. I have two motherboards with empty M.2 slots waiting for the market to catch up. I know about the XP941, but the pricing isn't great. M.2 drives should cost almost the same as a 2.5" drive...especially after eliminating the worthless metal/plastic box. Reply
  • extide - Monday, December 08, 2014 - link

    Seems to me like TLC will become the standard mainstream for 3D/VNAND, where as MLC will be pretty much only for high end/enterprise, somewhat like SLC was back in the day. Reply
  • MadDuffy - Monday, December 08, 2014 - link

    Newegg prices (USD) are up:
    120 GB - 90
    250 GB - 140
    500 GB - 250
    1 TB - 470

    Email I received indicates these are promotional prices available through Dec 14th
    Reply
  • casperes1996 - Monday, December 08, 2014 - link

    Last page, fifth paragraph, last line:
    "If I was"
    Should be: "If I were"

    I know I'm a cunt for pointing it out, but I only do so because I generally think Anandtech offers fairly decently written articles, and I care too much about this sort of piss...
    Sorry.
    Reply
  • apudapus - Monday, December 08, 2014 - link

    How is data retention with this type of TLC NAND? Can the drive be powered off for a week or a month before data gets corrupted? While the drive is powered on, I assume there are refresh features for stale (a.k.a. infrequently accessed) data. Reply
  • hojnikb - Monday, December 08, 2014 - link

    If its up to jedec (i imagine it is) then its good for atleast a year. Reply
  • kgh00007 - Monday, December 08, 2014 - link

    But in reality what are they going to be like? I don't think I'll buy another Samsung TLC drive after owning the 120 GB 840 EVO for the last while! It performs erratically, especially when resuming from hibernate. It can take anywhere from 10 secs to boot, up to 5 minutes, and I have applied the latest firmware and run the speed recovery app from Samsung. I have an mSata Crucial m500 240GB which is slower on paper, but in reality is much quicker and the performance is 100% consistent, it does the same thing, every time at the same speed!!

    MLC all the way for me without any turbowrite nonsense, just straight forward advertised speeds across the whole drive all the time, without loosing data due to poor charge retention along the way!
    Reply
  • Lolimaster - Monday, December 08, 2014 - link

    Your EVO is 120 and your other drive is 240, less nand, more erratic, simple. Look at the chart, you get consistent writes/read with 500-1TB models. Reply
  • kgh00007 - Saturday, December 13, 2014 - link

    Less nand equals slower performance, not more erratic performance. But it should perform at it's given speed consistentantly. I have over 30% of the drive free and 10% set as over provisioning on the 840 EVO. There is no excuse for a 5 minute boot time with an SSD. I don't trust these Samsung drives after my experience! Reply
  • mlkmade - Monday, December 08, 2014 - link

    So I'm confused as its not very clear...Is Turbowrite turned on for all your benchmarks?

    Is turbowrite needed to hit the the 540/520 read/write times? I saw the chart with TurboWrite on and off. So with turbowrite off this drive only gets 100mb/s ?

    This article is very vague in regards to that.
    Reply

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