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Samsung 845DC EVO SSD Review: 3-Bit MLC Hits The Enterprise
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1. Meet Samsung's Read-Focused 845DC EVO SSD

Sometimes a name is more than just a name, and you can glean a lot of information from the 845DC EVO's model number. As with Micron's M500DC and Intel's SSD DC S3500, the DC stands for data center. Normally, that implies the inclusion of power-loss protection, along with firmware optimized for enterprise workloads. And for anyone familiar with Samsung SSDs, the EVO suffix is a clear indication of what this drive is made of.

Before we get ahead of ourselves, Samsung's 840 EVO was released last summer to a host of good reviews. It offers good performance through some innovative technology, ships at high capacities, and sells for reasonable prices, largely due to its triple-level-cell NAND. Of course, during the past year, you couldn't even mention TLC flash without addressing inherently-lower write endurance, higher latencies, and reliability issues. And that was for a consumer-oriented SSD. Now we have Samsung launching a TLC-based drive for the enterprise market? That's right.

When TLC NAND was first productized, most would-be early adopters worried about its write endurance. Lower P/E cycle ratings scared a lot of folks, and when it came to the very lowest-capacity models, some of those concerns were founded. The issue is that judging an SSD's endurance based on the endurance of a single cell doesn't tell the whole story. Further complicating the situation, most enthusiasts think of two bit-per-cell MLC as good for 5000 to 10,000 cycles, which was true three to four years ago. But today's 20 nm MLC comes closer to 3000.

Although the physics of smaller manufacturing nodes whittles away at write endurance, SSD vendors are combating this in different ways. The first is simply adding more NAND. If the price of flash drops faster than the decrease in write endurance, more NAND can help compensate through greater over-provisioning or higher capacities. It's just simply math at that point, spreading writes out across more cells. Second, consider the ever-changing state of controller firmware. Wear leveling, garbage collection, and TRIM strategies have evolved dramatically, allowing SSD vendors to extend the usable lives of their drives. As a result, we concluded in Samsung 840 EVO SSD: Tested At 120, 250, 500, And 1000 GB that TLC is and should remain a viable technology for consumers. What we want to determine today is whether it's ready for a jump into big businesses.

Apparently, some of the misgivings about TLC hit home at Samsung. This time around, the company isn't calling its memory TLC. Rather, the 845DC EVO sports 19 nm Toggle 3-bit MLC NAND. Doesn't that sound better? And Samsung avoids the issue of write endurance by aiming its latest SSD at environments where reads are most prominent. This class of storage is becoming increasingly crowded; perhaps the most notable recent addition was Intel's SSD DC S3500.

Samsung 845DC EVO
User Capacity
240 GB
480 GB
960 GB
Interface
6 Gb/s SATA
Form Factor
2.5" 7 mm
Sequential Read
530 MB/s
Sequential Write
270 MB/s
410 MB/s
4 KB Random Read
87,000 IOPS
4 KB Random Write
12,000 IOPS
14,000 IOPS
Power Consumption(Active Max)3.8 W
Endurance (TBW)
150 TB
300 TB
600 TB
Reliability
2,000,000-hour MTBF
Warranty
Five years

The drive's specifications are competitive with other SSDs in the read-oriented space. More interesting, perhaps, is that we're being led to believe that the 845DC EVO beats Intel's potent SSD DC S3500 in almost every category, including endurance (despite the triple-level-cell memory). Intel only claims 140 TBW for its 240 GB model and 275 TBW for the 480 GB version.

At this point, the most significant spec missing is pricing. As with so many enterprise-focused launches, even after we reached out to Samsung for more information, we can't tell you what the 845DC EVO will cost. Consequently, it's going to be really tough to weigh in on its value. But let's put everything into perspective. When Samsung's SM843, the 840 Pro with enterprise tweaks, surface, its was priced aggressively in its segment. The drive sold for slightly more than an 840 Pro, in fact. If the company maintains this delta, the 845DC EVO could become an absolute steal considering that the 840 EVO, at larger capacities, consistently moves at less than $0.50/GB.

2. Inside Of Samsung's 845DC EVO

Opening up the 845DC EVO gives us flashbacks to our coverage of the 840 EVO. Its PCB and general layout, along with most of the components, are identical. Samsung's consumer-oriented 840 EVO employs a smaller PCB, which creates more empty space inside the 2.5" chassis. But the 845DC EVO's circuit board is larger to accommodate the power-loss protection capacitors, filling the enclosure.

Samsung's 845DC EVO uses the same MEX 400 MHz triple-core Cortex-R4-based controller (labeled S4LN045X01-8030) as the 840 EVO.

Also, the same 1 GB of LPDDR2 DRAM cache is present on the largest 845DC EVO model.

As mentioned in the introduction, Samsung's 845DC EVO employs 3-bit-per-cell NAND. Our 960 GB review unit includes 1024 GiB of raw flash capacity. Each of the on-board packages contains eight dies, with 16 GiB per die. The spare area (12.7%) is greater than what the 840 EVO (9.05%) offers, helping improve consistency and extend the NAND's life.

In the above shot, you can see some of the 23 power-loss capacitors used to keep the SSD's controller running just long enough, in the event of an outage, to flush all pending writes.

Overall, Samsung appears to take a direct approach to the 845DC EVO's design, only making changes deemed absolutely necessary. After all, the 840 EVO is already a fairly mature platform.

3. How We Test Samsung's 845DC EVO SSD
Test Hardware
ProcessorIntel Core i7-3960X (Sandy Bridge-E), 32 nm, 3.3 GHz, LGA 2011, 15 MB Shared L3, Turbo Boost Enabled
Motherboard
Intel DX79SI, X79 Express
Memory
G.Skill Ripjaws Z-Series (4 x 4 GB) DDR3-1600 @ DDR3-1600, 1.5 V
System Drive
Intel SSD 320 160 GB SATA 3Gb/s
Host Bus Adapter
LSI SAS 9300-8e
Tested Drives
Samsung 845DC EVO 960 GB
Comparison Drives
Micron M500DC 800 GB
Micron P400m 200 GB
Intel SSD DC S3500 480 GB
Intel SSD DC S3700 800 GB
SanDisk Optimus Eco 400 GB
Seagate 600 Pro 200 GB
Graphics
AMD FirePro V4800 1 GB
Power Supply
OCZ ModXStream Pro 700 W
System Software and Drivers
Operating SystemWindows 7 x64 Ultimate
DirectXDirectX 11
DriverGraphics: AMD 8.883
Benchmark Suite
Iometer v1.1.0
Four Workers, 4 KB Random: LBA=Full, Span Varying Queue Depths
ATTO
v2.4.7, 2 GB, QD=4
Custom
C++, 8 MB Sequential, QD=4
Enterprise Testing: Iometer Workloads
Read
Write
512 Bytes
1 KB
2 KB
4 KB
8 KB
16 KB
32 KB
64 KB
128 KB
512 KB
Database
67%
100%
n/a
n/a
n/a
n/a
100%
n/a
n/a
n/a
n/a
n/a
File Server
80%
100%
10%
5%
5%
60%
2%
4%
4%
10%
n/a
n/a
Web Server
100%
100%
22%
15%
8%
23%
15%
2%
6%
7%
1%
1%

The Storage Networking Industry Association (SNIA), a working group made up of SSD, flash, and controller vendors, has a testing procedure that attempts to control as many of the variables inherent to SSDs as possible. SNIA’s Solid State Storage Performance Test Specification (SSS PTS) is a great resource for enterprise SSD testing. The procedure does not define what tests should be run, but rather the way in which they are run. This workflow is broken down into four parts:

  1. Purge: Purging puts the drive at a known starting point. For SSDs, this normally means Secure Erase.
  2. Workload-Independent Preconditioning: A prescribed workload that is unrelated to the test workload.
  3. Workload-Based Preconditioning: The actual test workload (4 KB random, 128 KB sequential, and so on), which pushes the drive towards a steady state.
  4. Steady State: The point at which the drive’s performance is no longer changing for the variable being tracked.

These steps are critical when testing SSDs. It’s incredibly easy to not fully condition the drive and still observe out-of-box behavior, which may lead one to think that it’s steady-state. These steps are also important when going between random and sequential writes.

For all performance tests in this review, the SSS PTS was followed to ensure accurate and repeatable results.

All tests employ random data, when available. Samsung's 845DC EVO does not perform any data compression prior to writing, so there is no difference in performance-based data patterns.

For comparison purposes, we evaluated the 845DC EVO against similar products from Micron, Intel, SanDisk, and Seagate.

4. Results: Write Endurance Testing

Over the past few years, we've added a lot of write endurance testing to our benchmark suite. The rise of read-focused enterprise drives made those metrics even more important. Fortunately, during the last 12 months, testing enterprise SSDs standardized partly due to the introduction of JEDEC's JESD218A write endurance testing standard. Instead of issuing vague ratings, we now see companies specifying their drives to JESD218A, which uses the JESD219A enterprise workload to quantify endurance. The good news from all of that is that this closely matches the types of workloads we use in our Enterprise Workload Performance tests.

Previously, our write endurance testing consisted of large block sequential writes, which is completely different from the JEDEC standard. Still, it gives us valuable information about P/E cycles and allows us to compare SSDs at a NAND level, reducing the effects of flash controller optimizations and over-provisioning. Write amplification is also reduced so that we don't incur any additional NAND writes beyond what we intend.

For this test, we use the 240 GB model and monitor SMART attribute 177, which is the wear leveling count. It's a normalized value meant to show a percentage of life remaining on the drive. We took multiple percentage points off of the drive and compiled the results. We then extrapolated the number out to a full 100% usage; the following numbers are what we ended up with:

Endurance Rating
Sequential Workload, QD=1, 8 MB
Samsung 845DC EVOIntel SSD DC S3500
NAND Type
Samsung 19 nm 3-bit MLC
Intel 20 nm MLC
Raw NAND Capacity
256 GB
528 GB
IDEMA Capacity (User Accessible)
240 GB480 GB
Over-Provisioning
12.7%15.5%
P/E Cycles Observed (IDEMA)
3643
3651
P/E Cycles Observed (Raw)
3181
3097
Host Writes per 1% of MWI
7.95 TB
15.97 TB

As you can see, the 845DC EVO actually does get more P/E cycles (according to SMART) with Samsung's 3-bit MLC than we observed from Intel's SSD DC S3500.

Does that sound too good to be true? Let's change things up a but, then. Instead of using large block sequential writes, we'll go with 4 KB random writes instead, which should get closer to the JEDEC specification and apply more stress to the NAND/controller. Also, in this test we'll use the 960 GB model to see if the difference in over-provisioning matters.

The 687 TBW result ends up being mostly the same. Still, you're getting almost 15% more than Samsung's 600 TBW specification. That doesn't come anywhere close to eMLC flash or some of the optimized MLC-based solutions from SanDisk and Micron, but considering the price and target segment, it is more than adequate.

I'm also not taking into account that many review sites, including this one, have already pushed their consumer 840 EVO drives far beyond the point at which the wear leveling count hits zero. We hope our testing helps convince some of the doubters, but we can appreciate skepticism amongst a high-end audience.

5. Results: 4 KB Random Performance And Latency

Samsung's 845DC EVO is an absolute monster when it comes to random, small block reads. We easily hit the 87,000 IOPS that the drive is specified for. Only SanDisk's SAS-based Optimus Eco is able to top the 845DC EVO in this test.

Results are much more muted in our random write testing. Though they're still above Intel's SSD DC S3500, the 845DC EVO has a harder time keeping up with more expensive drives.

The outlier is Micron's M500DC, which achieves nearly twice as much performance and is in a similar price range.

The average response time lines up with the random write performance, observed above. That's to say Samsung's 845DC EVO lands near the bottom of the pack.

This chart is much more interesting. The 845DC EVO reports back a great maximum response time result, which is less than half of its nearest competitor.

New from Samsung is a stated Quality of Service (QoS) specification, closely matching what Intel publishes. This figure stipulates that 99.9% of write operations should be under 7 ms. We observed that 100% of all operations completed in under 7.31 ms, coming exceedingly close.

6. Results: Performance Consistency

We also pay a lot of attention to the performance consistency of enterprise-class SSDs. This is what separates a good drive from a great one when all of the corner case testing appears equal. Viewing the data with more granularity gives us insight on particular drive behaviors.

For the following tests, Samsung's 845DC EVO and three comparison SSDs are subjected to 25 hours of continuous random 4 KB writes. We record IOPS every second, giving us 90,000 data points. We then zoom in to the last 60 minutes to more coherently visualize the results.

The 845DC EVO demonstrates good consistency in our latency tests, surpassing Intel's SSD DC S3500 and Samsung's own SM843. It isn't able to keep pace with Micron's M500DC, which is still a steal considering $/IOPS. 

Samsung can be proud that more than 98% of all 1 s averages are better than the 14,000 IOPS specification. In fact, the lowest 1 s average is over 13,000 IOPS, which is still good for this market segment.

The histogram shows us a clean distribution without any major outliers. In this view, we see that the data points form an almost perfect bell curve, with the overall average latency contained within the largest bin of the histogram.

Looking at the first nine hours of write testing shows us that the 240 and 960 GB models perform similarly. You can see the effect of having more available NAND for over-provisioning, though. The 240 GB model exits its fresh-out-of-box condition and enters steady-state much more quickly than the 960 GB model. In fact, that latter implementation doesn't hit steady state until 12 hours after we begin the tests.

I also observed that, during the first 50 minutes, while still in the fresh out of box state, Samsung's 845DC EVO hit an incredibly stable 80,000 IOPS.

7. Results: Enterprise Workload Performance

Our next set of tests simulates different enterprise-oriented workloads, including database, file server, Web server, and workstation configurations.

The database workload (also categorized as transaction processing) involves purely random I/O. Its profile consists of 67% reads and 33% writes using 8 KB transfers.


The database profile normally rewards SSDs with strong random write performance. It puts the 845DC EVO near the bottom of the pack, though ahead of Intel's SSD DC S3500.

In the file server workload, which consists of 80% random reads of varying transfer sizes, the 845DC EVO narrows the gap. However, it still trails the drives offering better random write throughput.

The Web server workload (100% reads of varying transfer sizes) is more to the 845DC EVO's liking; the purely read-based test allows Samsung's latest to stretch its legs. Only SanDisk's SAS-based Optimus Eco tops it in this round of testing.

Finally, the workstation benchmark (80% reads, 80% random), which introduces write operations back into the mix, pulls the Samsung SSD back to the middle of the pack.

Overall, the 845DC EVO does really well in read-intensive applications. Once writes, even at a low percentage, are mixed in, Samsung succumbs to SSDs with better random write specifications. 

8. Results: Sequential Performance

The sequential results aren't much different than our previous tests. Write performance is decidedly middle-of-the-road, while read performance is class-leading. When Samsung said it was going after the read-heavy enterprise space, the company wasn't kidding.

9. Results: Enterprise Video Streaming

Video streaming is a demanding workload within the enterprise space. Companies want more HD streams with higher bit-rates and no stuttering. A storage solution well-suited for enterprise-class video delivery has completely different capabilities than something designed for databases. At the end of the day, you're basically looking for exceptional large-block sequential write performance. You also need a high level of consistency that traditionally isn't seen from consumer SSDs. For a more in-depth analysis, take a look at page 10 of Intel SSD 910 Review: PCI Express-Based Enterprise Storage.

Our large block sequential write testing closely matches the results from our performance consistency testing, which used small blocks and random accesses. The distribution of data points is very compact, with no signs of performance dips. This is another great sign that Samsung's transition from consumer platform to enterprise was a smooth one in its 845DC EVO.

10. Results: Power Consumption

In our Micron M500DC review, we detailed our new power consumption testing. In short, we apply varying workloads to the SSD we'r benchmarking and then measure the current draw using a high-resolution, high-precision industrial power source. Using this hardware, we can achieve millisecond resolution for our power measurements, allowing us to observe even slight changes in consumption.

As you can see from our power profile, Samsung's 845DC EVO does not pull down much power under our workloads. Even during random writes, the maximum power draw we observed was right at 3 W.

If you are looking for a drive that has a low active idle, this probably isn't the drive for you (even though our measurements come in under the 1.5 W specified by Samsung's datasheet).

Overall, the 845DC EVO posts some of the lowest power levels in the field, bested only by its sibling, the SM843. Hopefully this helps make up for higher idle consumption, especially since enterprise-oriented SSDs typically have a much higher duty cycle than consumer SSDs.

11. Samsung Introduces 3-Bit MLC NAND To The Enterprise

Samsung took a fairly straightforward approach to the introduction of its 845DC EVO: start with the 840 EVO consumer SSD, add power-loss protection, and tweak the firmware for enterprise workloads. Many other storage vendors have gone down a similar path. So, this re-purposing isn't out of the ordinary. Even still, I want to commend Samsung's execution.

Achieving over 14,000 sustained steady-state write IOPS, the 845DC EVO performs consistently well. But what really caught my eye was read performance. We easily hit Samsung's 87,000 IOPS specification. Sequential read throughput is also excellent. Best-in-class, even. Given the price range the 845DC EVO is expected to occupy, you won't find a better performer. Performance is truly maximized for this real-focused target market.

As with every enterprise buying decision, use case and price are both going to be major factors in determining whether Samsung's 845DC EVO is the right SSD. The drive should show up for well under $1/GB, and the closer that Samsung gets to 840 EVO pricing, the better. For its intended purpose of read workloads, you just can't beat the speed. If your application relies on any amount of write performance, pricing will weigh more heavily on the decision. Should that be the case, there are other enterprise-class SSDs like Micron's M500DC hovering around $1.15/GB offering superior write performance.  

[UPDATE - Samsung reached out to us after publication confirming that the 845DC EVO 240, 480 and 960 GB models will be priced at $249.99, $489.99 and $969.20, respectively.  While this is higher than we expected, it is still one of the most cost effective enterprise SSDs on the market.  Expect that number to drift lower over time and with volume purchasing]

Even with, presumably, great pricing and performance, some customers will still shy away from the 845DC ECO simply because of its TLC, er, 3-bit MLC NAND. Samsung is betting that a year's worth of reviews and endurance testing on the 840 will alleviate those concerns. At this point, we believe that 3-bit MLC is ready for entry-level, read-focused enterprise use. The important point is to know your workload. If your application matches what the 845DC EVO can do, we think you'll be pleasantly surprised at how well the drive fares.