SSD manufacturers are under constant pressure to reduce prices and increase capacity, but the pace of Moore's Law is never enough to satisfy consumers. As the SSD industry has matured, manufacturers have turned to other strategies for driving down costs, making tradeoffs to better suit what customers want. Early on, we saw a shift from single bit-per-cell SLC NAND to two bit-per-cell MLC, doubling capacity for the same size of chip (and therefore, cutting cost per GB in half). Currently, the industry is transitioning to 3D NAND techniques that allow for more storage capacity on a chip of a given size without requiring circuit elements and memory cells to shrink. Portions of the market are also shifting to use three bit-per-cell TLC NAND to get another capacity boost.

None of these advancements in storage density come for free. 3D NAND requires major changes to the manufacturing process, which is why only one of the four NAND manufacturers is currently shipping products with 3D NAND. Likewise, cramming more bits into the same memory cell has reprecussions. The more closely spaced voltage levels in the flash cells requires more careful control and more complicated error correction. It makes reading and especially writing slower, drives up power consumption and decreases durability. Everyone in the industry has struggled to create TLC-based SSDs that can compete on anything other than cost. Samsung has made the most use of TLC, aided by their lead in 3D NAND, but their TLC drives have had issues that have proven tough to stamp out. Despite the difficulty, most manufacturers now feel that TLC has a place in the market and that the downsides can be mitigated enough to suit consumers.

This brings us to Crucial's latest drive, the BX200. As the successor to the very successful BX100, it is a value-oriented 2.5" SATA drive. The BX200 moves to the newer Silicon Motion SM2256 controller and is Crucial and Micron's first TLC drive, using Micron's 128Gb 16nm TLC NAND. Micron's 16nm TLC was announced in June as intended for consumer applications. With a shift to 3D NAND planned for 2016, their 16nm TLC is something of a stopgap solution to further cut costs while temporarily stuck at the end of the road for planar NAND.

Silicon Motion's SM2246EN controller has been a popular choice for low-cost client drives, and when paired with MLC NAND it offers decent performance and very low power consumption. While it technically supports TLC NAND, only the successor SM2256 controller supports the more advanced LDPC error correction that is widely viewed as necessary to get sufficient reliability from a TLC drive. There are now several TLC drives on the market using the SM2256, competing primarily against each other and earlier SM2246EN drives with MLC, and MLC and TLC drives using Phison S10 controllers. Further up the price and performance scale are mid-range MLC drives and Samsung's TLC-based 850 Evo.

Crucial  480/500/512GB SSD Comparison
Drive BX100 BX200 MX200
Controller Silicon Motion SM2246EN Silicon Motion SM2256 Marvell 88SS9189
NAND Micron 16nm 128Gbit MLC Micron 16nm 128Gbit TLC NAND Micron 16nm 128Gbit MLC
Sequential Read 535 MB/s 540 MB/s 555 MB/s
Sequential Write 450 MB/s 490 MB/s 500 MB/s
4kB Random Read 90k IOPS 66k IOPS 100k IOPS
4kB Random Write 70k IOPS 78k IOPS 87k IOPS
Endurance 72 TB 72 TB 160 TB
Warranty 3 years

The BX200 specifications show only moderate performance increases over the BX100, except for the random read speed which is significantly decreased. The higher program and erase times of TLC NAND are probably the most difficult downside to mitigate, as SSDs have always been trying to compensate for their much higher latency than DRAM. Throughput can be increased by using multiple flash chips in parallel, but random read performance ultimately is limited by how long it takes the drive to fetch any data from the flash chips, so some decrease was probably unavoidable.

With the BX200 Crucial is retiring the 128GB capacity class. As flash memory gets cheaper, the fixed costs of the controller and other components come to dominate the budget and smaller capacity drives end up costing more per GB than mid-range capacities. Additionally, the smallest capacities have the least ability to provide parallelism, which can hobble their performance.

For most of the charts in this review, I've highlighted in blue the other TLC drives we've tested.

AnandTech 2015 SSD Test System
CPU Intel Core i7-4770K running at 3.5GHz (Turbo & EIST enabled, C-states disabled)
Motherboard ASUS Z97 Deluxe (BIOS 2501)
Chipset Intel Z97
Chipset Drivers Intel 10.0.24+ Intel RST 13.2.4.1000
Memory Corsair Vengeance DDR3-1866 2x8GB (9-10-9-27 2T)
Graphics Intel HD Graphics 4600
Graphics Drivers 15.33.8.64.3345
Desktop Resolution 1920 x 1200
OS Windows 8.1 x64
Performance Consistency
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  • FalcomPSX - Tuesday, November 03, 2015 - link

    SLC NAND stores one bit per flash cell. MLC stores two bits per cell. and TLC stores three bits per cell. Reply
  • zeeBomb - Sunday, November 08, 2015 - link

    Less bits the better? Reply
  • Dahak - Tuesday, November 03, 2015 - link

    So I had primarily just skimmed the article, but for a successor to the BX100 its not.
    I wonder if there is some firmware bug that might be causing an issue.

    I have used the BX100s fine in general office settings, but i many need to pass on these and start to look for an alternative
    Reply
  • mczak - Tuesday, November 03, 2015 - link

    Honestly I think the BX200 as a cheap SSD makes sense. The problem with the BX100 was that it was "too good". There was just about no difference in performance to the MX200 (faster in some benchmarks even), there was some feature differences (for instance no AES encryption, albeit this seems to have been an artificial firmware limitation as the controller supports it) but who cares about that in client ssds. But on the downside, there was just about no price difference to the MX200 neither, some shops selling some capacities of the BX100 actually for more than the same capacities for the MX200 sometimes. So the Crucial BX100 and MX200 were really pretty much the same in nearly all aspects.
    But with BX200 this changes - the MX200 now clearly is the better product, but the BX200 definitely is cheaper (or at least retail prices really need to be cheaper). Albeit the benchmarks are definitely concerning - even with tlc nand it shouldn't be THAT bad, maybe indeed the firmware is to blame.
    Reply
  • hojnikb - Tuesday, November 03, 2015 - link

    Actually, TLC is pretty bad and is mostly the sole reason why this drive performs so badly. Remove the SLC cache and it would be much worse (especially on paper). Reply
  • mczak - Tuesday, November 03, 2015 - link

    I don't quite agree. There's other tlc nand ssds in the benchmarks. Even if you exclude the 850 Evo (with its 3d nand) there's still the (toshiba tlc nand based) ocz trion 100. And this performs quite ok - sure it's not exactly leading but it doesn't trail by huge amounts in some benchmarks like the bx200 does. I'd have expected the bx200 to perform close to that rather than a league of its own as far as slow ssds go... I don't know though if that's due to differences between toshiba tlc and micron tlc or if that's due to controllers. Reply
  • Drumsticks - Tuesday, November 03, 2015 - link

    It can't be *just* the NAND. The other TLC based drives in the charts perform much closer to "mainstream" than "absolutely terrible at everything" Reply
  • hojnikb - Tuesday, November 03, 2015 - link

    its pretty hard to make good tlc. so yeah, tlc from micron simply sux. no other way around it.

    its no controllers fault, as it should perform just fine on its own, since its based off *46
    Reply
  • DanNeely - Tuesday, November 03, 2015 - link

    Assuming the street price does settle in at a reasonable discount to MSRP (and thus is cheaper than most other budget drives), these look like a reasonable option for office work. It look ~4 minutes of sustained full writes for the 480GB model to choke. Outside of photo/video editing the only time a normal user is going to hit that long of a sustained write is for OS or very large software installs. The rest of the time, most writes will be a few seconds at most before an idle period gives the drive time to catch up and flush the ram/SLC caches; meaning they should mostly sit in the (short) burst where the drives IO is similar to what much higher end drives achieve; and most longer operations will still fit in the middle plateau which is similar in performance to most budget drives on the market. Reply
  • beginner99 - Tuesday, November 03, 2015 - link

    Too expensive or too low performance. I think everyone can afford that $20 to step up to a MX200 or similar. And this $20 is more than worth it given the extra performance. Off topic but I would also like how older SSDs fare in these benches just as a comparison. Say I have an intel G2, will I actually gain anything noticeable from moving to a new SSD? Reply

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