Next Gen NVMe SD Card Review: The SM2708 Controller Serves it Hot and Fast
by Ganesh T S on September 9, 2021 9:00 AM EST- Posted in
- Storage
- NAND
- flash
- NVMe
- Silicon Motion
- Memory Cards
- 3D TLC
- SD Express
Long-Term Performance Evaluation
A few of the benchmarks are repeated on the memory card after subjecting it to the extended usage simulation.
Sequential Access - fio Workload
Re-processing the fio workload in the used mode gives an idea of long-term performance consistency (whether there is appreciable degradation in performance as the amount of pre-existing data increases and / or the card is subject to wear and tear in terms of amount and type of NAND writes).
| fio Sequential Workload [Used] | |
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In the SD Express mode, the card's SLC cache has essentially run out by the time the workload starts for the used case. So, we do not see the ~375MBps level seen in the fresh pass. However, there is no drop to 30 MBps either, as the card is able to maintain a steady 75 MBps almost all through. In fact, the fio workload completed faster to fill up 90% of the card capacity in the used pass compared to the fresh pass. The reads are slightly slower in the used pass, but the relative variations are similar. In the UHS-I mode, the writes start slower in the used pass, but the consistency is better compared to the fresh pass - essentially similar to the SD Express case. Reads are consistent in both passes at around 70 MBps.
Performance Restoration - CrystalDiskMark
The traditional memory card use-case is to delete the files on it after the import process is completed. Some prefer to format the card either using the PC, or, through the options available in the camera menu. The first option is not a great one, given that flash-based storage devices run into bandwidth issues if garbage collection (processes such as TRIM) is not run regularly. Different memory cards have different ways to bring them to a fresh state. Silicon Motion specified that SD Express cards need to be formatted in NVMe mode in order to restore performance.
In order to test out the effectiveness of the performance restoration process, we run the default sequential workloads in CrystalDiskMark before and after the formatting. Note that this is at the end of all our benchmark runs, and the card is in a used state at the beginning of the process.
| CrystalDiskMark [Used] Benchmarks | |
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In the used pass, the reads drop from 890 MBps to 733 MBps, and writes from 418 MBps to 95 MBps for the sequential workloads in the SD Express case. Other access traces see similar drops. The UHS-I case also sees a similar drop in relative performance.
| CrystalDiskMark [Refreshed] Benchmarks | |
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Upon formatting in SD Express mode, the performance gets restored to around 878 MBps / 415 MBps). However, formatting in UHS-I mode has no effect, as the refreshed CrystalDiskMark numbers are very similar to the numbers seen in the used case.
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nandnandnand - Thursday, September 9, 2021 - link
I've asked this question myself. The volume of an SD card is about 10x that of a microSD card. You would expect it to be able to fit 4x, maybe 8x as much NAND. The largest capacity for both is still stuck at 1 TB.The first thing to do would be to go to 2 TB since it would be compatible with SDXC readers. After that, what is the market for SDUC? Some smartphones are dropping the microSD slot as the internal storage is now "good enough". Videographers may want an 8 TB full-size SD card, probably with SD Express speeds to deal with 4K/8K/360-degree video capture. Maybe the card needs to be made out of aluminum for cooling.
meacupla - Thursday, September 9, 2021 - link
If I had to guess, there is a limitation at the controller and/or reader.I doubt there is a problem with file format type, as exFAT has existed for a while now, with very high compatibility, and even if the format type was limited to FAT32, the maximum size would be 2TB
schuckles - Friday, September 10, 2021 - link
I think that pretty much all designs for SD cards attempt to support micro SD as well. So in the end the bigger size is more about consumer use case than increased capacity.nandnandnand - Friday, September 10, 2021 - link
All of the devices that support a full sized SD card should be compatible with a microSD adapter card, and pretty much all microSD cards I've seen come with an adapter (I have at least 14 of them now).There's no technical reason for SD cards to not be available in higher capacities, it comes down to the nature of the market. Maybe 10-100 times more devices are compatible with microSD because of smartphones. I wouldn't be surprised if a 2 TB microSD card gets announced before a 2 TB full-sized SD.
Nevod - Saturday, September 11, 2021 - link
Yes, there's no reason to develop additional functionality for full-size SD as market is much smaller than for microSD.Hopefully, SD Express readers may appear on notebooks and become a decent performance option to increase storage. That may provide a push to increase full-size card capacity, if price would be competitive with m.2 and USB options.
nandnandnand - Saturday, September 11, 2021 - link
I am hopeful. I've seen SD card readers on even OEM desktops I've looked at lately, and controllers like this are available:https://www.anandtech.com/show/16603/silicon-motio...
Xajel - Thursday, September 9, 2021 - link
I think one major test is left out here, performance per watt.I mean for a portable device, power is crucial here, if at that speed the card can save the exact same file much faster than a non-SD 7.1 card and eventually consumes less power then it's a win for the portable device. They can use it and get faster while consuming less power because it needs less time to save the data.
But if if the Performance/Watt was low then it's a problem, And maybe they will use a custom firmware to actually limit the performance to save power and stay within the required temperature. And the smaller the device the more crucial is to stay within low power/temp. Like mobile devices.
Using microSD Express might as well save Android from getting rid of the expandable storage due to lack of good performance on current microSDs (very low IO performance).
nandnandnand - Thursday, September 9, 2021 - link
"Using microSD Express might as well save Android from getting rid of the expandable storage due to lack of good performance on current microSDs (very low IO performance)."That would be nice, but I think the major manufacturers just want to get rid of it so they can sell you a phone with 1 TB UFS for $200 more.
meacupla - Thursday, September 9, 2021 - link
I am surprised the controller is still using 28nmdoesn't that take up a lot of space?
beginner99 - Friday, September 10, 2021 - link
"We are bullish..." Dude this isn't some hipster crypto forum...