Samsung SSD 870 QVO in the test: Lots of space and performance up to the QLC brake
tl; dr: Samsung's SSD 870 QVO, the second generation of the QLC SSD, hardly behaves differently than its predecessor 860 QVO in the test, despite the change in memory and controller. This means that writing large amounts of data beyond the SLC cache remains the Achilles heel - however, standard benchmarks do not record them.
To better classify the test results, the article has been supplemented with measured values from a classic hard drive (HDD) of the Western Digital Black 6 TB (WD6001FZWX) type.
Samsung's second generation of the QLC SSD
With the SSD series 860 QVO (test) , Samsung used its own QLC NAND flash for the first time at the end of 2018 4 bits per memory cell. The abbreviation “QVO” stands for “Quality and Value Optimized”, which indicates the low costs with the new QLC memory, which forms the basis for inexpensive mainstream SSDs with SATA connection.
QLC-NAND offers a higher storage density and long termlower cost per bit, which should make products like SSDs and memory cards cheaper. However, QLC-NAND is potentially slower and less durable than its direct predecessor (TLC with 3 bit), which is at least partially compensated for by technical measures such as a write buffer and extensive error correction.
The first client SSD with 8 TB? Not quite!
The Samsung 870 QVO follows this scheme, but compared to the 860 QVO it uses a newer QLC memory and a new controller. With this, the manufacturer not only promises more performance, but also doubles the storage space of the top model from 4 TB to 8 TB.
On the fact that this is currently the 'largest client SSD in the world', as Samsung claims , howeverargue, because Sabrent has recently started offering the Rocket Q, an 8 TB SSD in the M.2 form factor . Actually from the enterprise segment for servers, the Micron ION 5210 in the same format as the Samsung 870 QVO also has only slightly less storage space of 7.68 TB, but is also used by private customers and is therefore included similar technology as a secret competitor of the 870 QVO with 8 TB.
The Austrian provider Angelbird has also already received a 2nd , 5-inch SSD with 8 TB for consumers, but the availability is currently not given and the price is extremely high .
New features compared to the 860 QVO
New controller and new memory
Compared to the 860 QVO withSamsung uses 64-layer QLC-NAND and MJX controllers for the 870 QVO on 96-layer QLC-NAND (V-NAND V5) and an MKX controller labeled S4LR059 is. Samsung does not disclose details about the controller, but it should use an error correction algorithm that has been improved compared to its predecessor. The NAND packages are labeled with K9XVGB8J1 A , which distinguishes the 96-layer generation from the 64-layer chips (K9XVGB8J1 M ). The test pattern with 4 TB of useful memory has four NAND packages distributed on both sides of the board, which thus each offer 1 TB of storage space and combine eight 1,024 Gbit dies. Spaces for four additional chip housings are reserved, which are then also equipped in the 8 TB model. The 4 GB oneLPDDR4 DRAM cache sits right next to the controller. There is practically no difference in the layout to the 860 QVO, which also uses 1 TB NAND packages.
The PCB of the Samsung SSD 860 QVO with 4 TB already offered four more slots for NAND - an 8 TB version never appeared in this series.
Slight performance increases
The new components should provide more performance. Specifically, Samsung promises marginally higher sequential transfer rates (in the SLC cache) of up to 560 MB/s reading (860 QVO: 550 MB/s) and 530 MB/s writing (860 QVO: 520 MB/s) and around 13 percent more IOPS for random reading (4K Random Read) with a practical command queue from QD1. Under continuous load ('sustained performance'), the performance in random writing should also be higher. The rather theoretical maximum QD32 values for private users are almost unchanged.
In this context, however, Samsung points out a change in the values for the 860 QVO: The manufacturer benchmarks have now been switched to Windows 10 becauseMicrosoft has officially discontinued support for Windows 7 . However, there is a higher latency when writing to the SSD under Windows 10 than under Windows 7, which is why the 4K Write IOPS are now lower.
There are no changes in the area of the guarantee: The 870 QVO offers a maximum of three years guarantee;Bytes Written '(TBW), which is again 360 TB per terabyte of storage capacity. For the test pattern with 4 TB, this means 1,440 TB of written data until the guarantee expires.
8 TB means 8 GB of DRAM cache
In addition to the controller and NAND flash, there is also the DRAM -Cache with Samsung SSDs always from our own production. As with various series before, the manufacturer relies on economical LPDDR4 memory. The company remains true to the rule of thumb “1 GB DRAM per 1 TB NAND flash”, so that the 8 TB model has a full 8 GB LPDDR4. With increasing storage capacities, there is also a growing need for DRAM in SSDs. For the time being, Samsung is not going the way of a so-called DRAM-less SSD, in which this buffer memory is dispensed with for cost reasons.
Pseudo-SLC cache alias TurboWrite
There is also no change in the SLC write buffer compared to the 860 QVO. A small portion of 6 GB is fixed and is therefore always available. If the memory that is not occupied with user data is large enough, 36 GB or 72 GB dynamic SLC cache are added. From 2 TB the size of the dynamic cache does not increase any further, so that the 8 TB model also has a maximum of 78 GB SLC cache (6 GB + 72 GB).
The write performance after the SLC cache is also unchanged: Even the 870 QVO 8 TB with twice as much storage space then only achieves 160 MB/s with sequential Write. A higher write performance through more parallel access to more memory chips does not apply here. The second generation of the QLC-NAND from Samsung does not offer any advantages in this respect.
However, Samsung advertises that the memory cells reserved for the fixed SLC cache have a longer shelf life. The change from 64 to 96 layers should increase the 'SLC endurance' by a factor of 3.8.
Specifications: 870 QVO vs. 860 QVO
The direct comparison of the specifications according to the manufacturer clarifies the minor differences between Samsung 870 QVO and Samsung 860 QVO. Despite the change in storage and controller, the 8 TB model remains the biggest innovation, at least with these key data.
On the next page: Test results and conclusion
