When we first starting seeing PCIe-based storage in the enterprise market, it was obscenely expensive. Tens of thousands of dollars per device was not unheard of. But like all flash-based products, prices dropped and they continue to do so. Some of this has to do with shrinking feature geometry. However, manufacturers are also getting more strategic about using the right flash technology for their products. If we were still looking at predominantly SLC- and eMLC-based drives, price per gigabyte would still be very high.
Now, we're talking about enterprise storage here, so write latency and endurance are factor very prominently in any discussion of performance. Many applications continue to demand the very best of the best. At the same time, IT managers are getting a lot smarter about how to apply solid-state tech to their workloads, which is why we're starting to see a lot more products built to deliver very fast reads at more economical prices.

This reflects a deliberate effort to break the enterprise SSD market into increasingly smaller and better-targeted pieces. Those read-focused SSDs represent one of the fastest growing segments because of how well-positioned they are. Typically, you get outstanding read performance from them, along with mediocre write throughput and endurance. In server caching applications, this trade-off is almost always worth it. They're so heavily weighted towards read operations that paying for equally great write performance isn't justified. And the trend is transcending 2.5" SSDs, carrying over to the PCIe-based storage market as well.
With the P420m's introduction, Micron is pushing MLC technology into its PCI Express-based product line. The two main benefits that come from using MLC NAND in 2.5" drives carry over: higher capacities and lower costs. Micron's P420m consequently serves to complement the P320h, which we reviewed in Micron RealSSD P320h Review: A PCIe Drive Capable Of 3.2 GB/s. To recap, the P320h is an SLC-powered monster that serves up excellent 4 KB read and write IOPS, along with great write endurance. It basically gives you all of the good attributes of single-level cell flash and PCI Express, along with the combination's greatest weakness, price. At $10/GB, the P320h is not cheap. Micron hopes that its P420m is more accessible without sacrificing performance.

The P420m is actually available in two different form factors. One is a 2.5" drive that connects via eight second-gen PCI Express lanes, and ships in 350 and 700 GB capacities. The second, which we're reviewing today, is a half-height, half-length (HHHL) PCIe-based add-in card, also communicating across eight second-gen lanes. This second version will surface in 700 and 1400 GB capacities, doubling the P320h's largest configuration.
As it does with most of its enterprise-oriented offerings, Micron is keeping pricing under wraps. Our sources tell us to expect less than $5/GB, though.
| Micron PCIe Product Lineup | |||||||
|---|---|---|---|---|---|---|---|
| Product | P420m | P320h | |||||
| Form Factor | HHHL | ||||||
| User Capacity (GB) | 700 | 1400 | 350 | 700 | |||
| Interface | x8 PCI Express 2.0 | ||||||
| Sequential Read (MB/s) | 3300 | 3200 | |||||
| Sequential Write (MB/s) | 600 | 630 | 1900 | ||||
| 4 KB Random Read (IOPS) | 750,000 | 785,000 | |||||
| 4 KB Random Write (IOPS) | 50,000 | 95,000 | 205,000 | ||||
| Power Comsumption (Active) | 22 W | 30 W | 25 W | ||||
| Power Consumption (Idle) | 8 W | 10 W | |||||
| Write Endurance (TBW) | 5 PB | 10 PB | 25 PB | 50 PB | |||
Based only on read performance, the difference between Micron's P420m and P320h is marginal, which is a good thing since the P320h excels in read tests. Given a significantly lower price tag, the P420m should represent a significantly better value in read-intensive tasks as a result.
Of course, write performance isn't as attractive. Although, while 95,000 random 4 KB write IOPS is quite a bit lower than the P320h's, that figure also represents the drive at steady state, whereas most mainstream SSD vendors cite fresh-out-of-box specifications.
Write endurance also takes a hit. Though, considering the rated specification is still 20% of the SLC-equipped drive, that's a really good sign.

Visually, the P420m is quite a bit different looking than the P320h. Micron choose to cover the entire power loss protection board with black plastic. With it removed, you clearly see that the complete drive is made up of three PCBs with a large heat sink sticking through two of them.

The first PCB has a little bit of everything, but we are going to focus on its flash controller. Micron is using the exact same processor as the one on its P320h. As we noted in Micron RealSSD P320h Review: A PCIe Drive Capable Of 3.2 GB/s, this controller was jointly produced with IDT and is customized to work specifically with Micron's NAND and firmware algorithms. Unlike most SATA/SAS controllers, which only support eight channels and 16 NAND placements, the P420m's controller has 32 channels and supports 64 placements. This extended parallelism facilitates the high read performance noted in the specifications. It's also one of the reasons why the P420m, like the P320h, doesn't hit its peak performance until a queue depth of 256.

We didn't have it in us to remove the heat sink. It's attached with a thin wire mesh covered by adhesive. Popping it off would almost certainly damage the mesh.

Next to the controller is a low-profile heat sink covering five DRAM packages, each of which adds 256 MB of DDR3-1600. There are four more on the back of the PCB, giving you a total of 2.25 GB on the P420m.

It'd be impossible to miss the 25 nm MLC flash, which is a major departure from the 34 nm SLC used on Micron's P320h. There are 28 NAND packages on the main PCB.

The next PCB's job is purely to host NAND and a handful of discrete components. This is where you'll find the remaining 36 packages (adding up to 64 in all). Do the math and we figure out that each package hosts eight 32 Gb dies. In contrast, the 700 GB model's packages each host four dies. This means the 1400 GB version has 2048 GB of raw flash on-board.

Micron's redundancy technology takes up roughly one-eighth of that number, or 256 GB. The rest, about 22%, is used for over-provisioning.

The third PCB handles power loss protection.

Our sample has 48 tantalum capacitors, with pads for many more. Unlike the substantial connector between the first and second boards, this power loss PCB is connected to the main one through a tiny eight-pin header.
The PCB is also extremely thin, presumably only a few layers thick. You could almost say it's fragile, which is why Micron secures it at five points to the rest of the drive. Power loss protection is one key feature that was missing from the P320h, and is a welcomed addition on the P420m.

Micron tends to make data protection a priority on its enterprise-oriented SSD products, and the P420m is no different. The company leverages its RAIN (Redundant Array of Independent NAND) technology, seen on the P320h and P400m, to enable RAID 5 redundancy across all flash channels. RAIN recovers lost data beyond just page-, block-, and die-level failures. The P420m also checks data using CRC (Cyclic Redundancy Checksums) and ECC (Error Checking and Correcting) algorithms prior to and upon exit from each element in the transfer chain.
Although the P420m and P320h don't look like each other physically, architecturally speaking, they might as well be twins.
| Test Hardware | |
|---|---|
| Processor | Intel 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 |
| Tested Drives | Micron P420m 1400 GB |
| Graphics | AMD FirePro V4800 1 GB |
| Power Supply | OCZ ModXStream Pro 700 W |
| System Software and Drivers | |
| Operating System | Windows 7 x64 Ultimate |
| DirectX | DirectX 11 |
| Driver | Graphics: ATI 8.883 |
| Benchmark Suite | |
| Iometer v1.1.0 | 4 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:
- Purge: Purging puts the drive at a known starting point. For SSDs, this normally means Secure Erase.
- Workload-Independent Preconditioning: A prescribed workload that is unrelated to the test workload.
- Workload-Based Preconditioning: The actual test workload (4 KB random, 128 KB sequential, and so on), which pushes the drive towards a steady state.
- 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. Micron's P420m does not perform any data compression prior to writing, so there is no difference in performance-based data patterns.

Even though the P320h has a slight edge on the datasheet, the P420m came away with a close win in random 4 KB read operations. Both drives absolutely torched the competition. Even the best enterprise-oriented SATA SSDs only hit 90,000 IOPS. You would need eight of them on an efficient RAID controller to come close to the 760,000 IOPS we see from the P420m.

A thread you're going to see from here on out in this story is strange write behavior, both good and bad, from the P420m. When it comes to random 4 KB writes, we end up on the good side. Normally, you need a medium-sized command queue to get writes up to spec. Far fewer than the reads, but still 16-32. The P420m hits its specification at a queue depth of one, though. It didn't seem to matter how many more commands we threw at it; performance remained constant.
Also good is that we're consistently over 110,000 IOPS, blowing past Micron's 95,000 IOPS specification. Again, the P420m tops Intel's SSD 910, but falls short of the P320h and OCZ Z-Drive. Considering the NAND technology and pricing of each device, this is what we'd expect.


The average response times line up well with the random write performance we saw above. Once again, nothing can touch the P320h when it comes to performance consistency. We're a little more troubled by the maximum response time reported by the P420m, though. Normally, high response times are what make us question consistency. On the next page, we will take a closer look.
In the following tests, we subjected our enterprise SSDs to 25 hours of continuous random 4 KB writes across each drive. We recorded the IOPS every second, giving us 90,000 data points. We then zoomed in to the last 60 minutes to more coherently visualize the results.

As you can see from the graph above, the P420m, while delivering high overall average IOPS, also produces some noisy results. Depending on your take, the P420m actually performs better than the P320h at a queue depth of 32. In terms of consistency, though, the P320h is still a far superior drive. At a queue depth of 256, the P320h takes a clear and commanding lead.

The consistency graph doesn't always tell the whole story because outliers show up more prominently than clusters of points. When looking at the histogram, you can see that roughly 70% of the data-points meet Micron's specification. Compare that to the P320h at a queue depth of 256, where 87% of the data points are at or above the specification, and 99% fall within 97.5% of its spec. Looking at the results differently, the P420m has a standard deviation of 16,000 IOPS, while the P320h's is only 4,000 IOPS.
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 P420m holds its own at lower queue depths, but can't keep up with Micron's flagship at higher queue depths. It does best Intel's SSD 910 though, eventually doubling its effort. The P420m owes a lot of its performance at lower queue depths to the flat random write performance across all queue depths.

In the file server workload, which consists of 80% random reads of varying transfer sizes, we see the same basic results. Micron's P420m once again runs out of steam against the P320h and the Z-Drive at higher queue depths, but nearly doubles the SSD 910.

Our Web server workload (100% read, varying transfer size), gives us a curious result. The P420m comes out on top across the board. We're going to chalk this up to our P320h not quite living up to its read specification on our test bench. In practice, both Micron drives should be about equal.

Finally, the workstation benchmark (80% reads, 80% random), shows the same general trend. Since the P320h and Z-Drive are not direct competitors, it's easy to write off any perceived shortcomings when comparing them to the P420h. The massive edge in read performance over Intel's SSD 910 shows up in our mixed workload tests, allowing the P420m to nearly double its performance.

As we've seen from our previous read tests, the P420m is a beast. There really isn't much more to say. Micron's latest delivers class-leading performance that even more expensive drives have a hard time matching.

Do you remember back to the specifications page, where we mentioned the curiously low sequential write performance? This is where it rears its ugly head. Really, the only positive thing to say is that the P420m reaches its maximum speed at small transfer sizes. Once you get past 32 KB blocks, the competition leaves Micron's P420m in the dust. Even Intel's SSD 910, which up until now posted 50% of the P420m's performance, nearly triples its sequential write speed.
Our only guess as to why the P420m has such low sequential write speed is that Micron tuned the firmware predominantly for small block, random performance, compromising sequential write performance.
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.
Once the drive is in a steady state, we write its entire capacity 100 times. We use 8 MB transfer sizes and a queue depth of four, recording timestamps for each individual write. The graph below reflects 100-point averaging, so that you can better visualize the results.

After 100 runs, there wasn't much of a difference between the best and worst. Both are well above the drive's specification. Those few dips that fall below would only require a few megabytes of buffer to overcome. Overall, the consistency is very impressive, but because the maximum sequential write speed is so low, we're left wanting more.
These results were only achieved after a lot of troubleshooting. Initially, we were seeing 800-1000 ms delays, from five to 30 times during every write. That's the sort of catastrophic failure that plagued the SSD business years ago. We tried multiple Intel motherboards and different test utilities, come up with the same numbers each time. We kept in constant contact with Micron, which provided much-appreciated support. Although we can't point our finger at a specific cause, it might be related to PCIe power states. When we added another PCIe device, the dips went away. Given that other devices (even Micron's P320h) didn't have any issues in the same configuration, we're not ready to rule out driver issues, either.
With the introduction of Micron's P420m, the company is gunning for enterprise customers with heavy read workloads. It's hoping that an MLC-equipped drive designed for such a purpose will attract attention with an aggressive price point.
Micron built the P420m with its P320h as a model, using many of the same components that made the P320h such a success. As before, Micron delivers a vertically-integrated product that it has complete control over, from the processor to the DRAM cache to the NAND flash.

After spending a few weeks with the P420m, we come away with the mixed feelings you'd expect from a device that was built for one purpose at the expense of others, though. Read performance is out of this world, for example. Once you start seeing consistent read IOPS in the 750,000 range and sequential throughput in excess of 3 GB/s, its hard to go back to 2.5" SATA drives. The P420m breezes through our enterprise workloads, only falling shy of Micron's P320h and the massive OCZ Z-Drive.
Our write tests aren't as definitively good or bad. We saw consistency in the 4 KB random transfer benchmarks at all queue depths. Write endurance is also a strong point for this MLC-based drive. But neither strength makes up for its sequential write performance. To be fair, Micron's specification is very low for this device's class, and there's no getting around that. In addition, we had issues with response times in our large block sequential transfers, leaving us with some valid concerns.

The P420m's ability to impress in read and mixed workloads is certainly notable, even in contrast to the compromises it makes trying to drive enterprise storage prices down. Professionals shopping for storage for data center caching, media streaming, and online transactional processing have a drive here that should exceed their expectations.