Almost all content capture devices employ memory cards (flash-based removable media) for storage. Hand-held consoles and many other computing systems (PCs as well as smartphones) also employ them for augmenting the available storage capacity. There are different varieties of memory cards catering to various performance levels. CompactFlash (CF) became popular in the late 90s. However, has now been overtaken by Secure Digital (SD) cards. In our series of memory card reviews, we recently looked at the PNY Elite microSDXC UHS-I 512GB, where we had mentioned that the SanDisk Ultra 400GB seemed to be priced much lower on a per-GB basis. We now have the performance numbers for the SanDisk card to enable us to understand the high-capacity microSDXC card market better.


SD (Secure Digital) cards were introduced in 1999, as an update to the existing MultiMediaCards (MMCs). It gained traction even in areas where CompactFlash had been preferred, thanks to its small size. Its popularity is evident by the fact that it has spawned two follow-ups in the same form factor - starting with the SDSC in 1999 for capacities between 1MB and 2GB, we got SD High Capacity (SDHC) in 2006 (up to 32GB) and SD eXtended Capacity (SDXC) in 2009 (up to 2TB). The cards also come in various sizes - standard, mini, and micro. Currently, the standard and micro sizes are more popular in the market. SD's popularity and affordability has meant that almost all consumer cameras come with a SD card slot.

Recently, we have seen a number of high-capacity microSDXC cards getting introduced. Starting with the 400GB SanDisk Ultra microSDXC UHS-I card ($94 at $0.23/GB) introduced in August 2017, we now have the Integral 512GB and the PNY Elite 512GB in the market as well. At Computex 2018, we also saw plans from ADATA and Team Group to sell 512GB microSDXC cards. With the industry migrating to 3D NAND, the capacity per die has seen significant increase, allowing for microSDXC cards to reach these capacities. The SanDisk Ultra microSDXC 400GB is a UHS-I card with a U1 (UHS Speed Class) / A1 (Application Performance) rating. Compared to the PNY Elite 512GB we reviewed earlier, the main difference is in the A1 rating that guarantees a minimum performance level in non-content capture scenarios (such as usage in smartphones). The A1 rating suggests that the card can sustain 10 MBps of sequential accesses, 1500 Read IOPS, and 500 Write IOPS.

SanDisk supplied us with a retail sample of their Ultra microSDXC 400GB card to put through our comprehensive memory card evaluation routine. Prior to taking a look at the performance numbers, we take a look at the testbed setup and evaluation methodology.

Testbed Setup and Testing Methodology

Evaluation of memory cards is done on Windows with the testbed outlined in the table below. The USB 3.1 Type-C port enabled by the Intel Alpine Ridge controller that connects to the Z170 PCH via a PCIe 3.0 x4 link is used for benchmarking purposes on the testbed side. uSD cards utilize the Lexar Professional Workflow SR2 SDHC / SDXC UHS-II USB 3.0 Reader along with the microSD to SD adapter supplied by the card vendor. The reader was placed in the Lexar Professional Workflow HR2 hub and uplinked through its USB 3.0 port with the help of a USB 3.0 Type-A female to Type-C male cable.

AnandTech DAS Testbed Configuration
Motherboard GIGABYTE Z170X-UD5 TH ATX
CPU Intel Core i5-6600K
Memory G.Skill Ripjaws 4 F4-2133C15-8GRR
32 GB ( 4x 8GB)
DDR4-2133 @ 15-15-15-35
OS Drive Samsung SM951 MZVPV256 NVMe 256 GB
SATA Devices Corsair Neutron XT SSD 480 GB
Intel SSD 730 Series 480 GB
Add-on Card None
Chassis Cooler Master HAF XB EVO
PSU Cooler Master V750 750 W
OS Windows 10 Pro x64
Thanks to Cooler Master, GIGABYTE, G.Skill and Intel for the build components

The full details of the reasoning behind choosing the above build components can be found here.

Sequential Accesses

SanDisk claims speeds of up to 100 MBps. However, real-world speeds are bound to be lower. In fact, writes can sometimes be much slower. For most applications, that really doesn't matter as long as the card is capable of sustaining the maximum possible rate at which the camera it is used in dumps data. We use fio workloads to emulate typical camera recording conditions. We run the workload on a fresh card, and also after simulating extended usage. Instantaneous bandwidth numbers are graphed. This gives an idea of 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). Further justification and details of the testing parameters are available here.

The read performance is close to the claimed numbers and similar to that of the PNY Elite 512GB card. The writes are much better - averaging around 40 - 50 MBps in both the fresh and the used passes. This compares much favorably to the PNY Elite's 22 MBps. There is a slight dip below 20 MBps in the used pass, but, that performance loss is typical of almost all memory cards which haven't been subject to performance restoration by formatting after extended usage.

AnandTech DAS Suite - Performance Consistency

The AnandTech DAS Suite involves transferring large amounts of photos and videos to and from the storage device using robocopy. This is followed by selected workloads from PCMark 8's storage benchmark in order to evaluate scenarios such as importing media files directly into multimedia editing programs such as Adobe Photoshop. Details of these tests from the perspective of memory cards are available here.

In this subsection, we deal with performance consistency while processing the robocopy segment. The graph below shows the read and write transfer rates to the memory card while the robocopy processes took place in the background. The data for writing to the card resides in a RAM drive in the testbed. The first three sets of writes and reads correspond to the photos suite. A small gap (for the transfer of the videos suite from the primary drive to the RAM drive) is followed by three sets for the next data set. Another small RAM-drive transfer gap is followed by three sets for the Blu-ray folder. The corresponding graphs for similar cards that we have evaluated before is available via the drop-down selection.

Typical of almost all memory cards, we see small files bringing down the write rates. The key takeaway here is that there is no consistency issue between two passes for the same data. That said, writing large files tends to show varying performance levels between 10 and 55 MBps (skewed towards the larger value) unlike the PNY Elite which comes in at 20 MBps balanced all through.

AnandTech DAS Suite - Bandwidth

The average transfer rates for each workload from the previous section is graphed below. Readers can get a quantitative number to compare the SanDisk Ultra microSDXC UHS-I 400GB uSD card against the ones that we have evaluated before.

Photos Read

We also look at the PCMark 8 storage bench numbers in the graphs below. This gives an idea of how the cards would behave in a relative manner when subject to application workloads. Note that the bandwidth number reported in the results don't involve idle time compression. Results might appear low, but that is part of the workload characteristic. Note that the same testbed is being used for all memory cards. Therefore, comparing the numbers for each trace should be possible across different cards.

Adobe Photoshop Light Read

The performance numbers here reflect the speed class rating of the card. The SanDisk Ultra is not the fastest UHS-I card - the SanDisk Extreme trumps it, albeit at a lower capacity point. Like the PNY Elite, the SanDisk Ultra is not a speed play. Rather, it is a capacity play, which is not reflected well in this evaluation segment.

Performance Restoration

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.Based on our experience, uSD cards have to be formatted using the SD Formatter tool from the SD Association (after all the partitions are removed using the 'clean' command in diskpart).

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. The corresponding screenshots for similar cards that we have evaluated before is available via the drop-down selection.

We do see a drop in the write rate after performance restoration, with numbers similar to what we see in the sustained write workload. The performance is still better than the requirements of the claimed speed rating.

Concluding Remarks

The SanDisk Ultra microSDXC UHS-I 400GB card successfully completed our intensive benchmarking routines. It showed better performance numbers than the PNY Elite - the only other high-capacity microSDXC card that we have reviewed. However, in terms of raw benchmark numbers, it emerged as an average performer in the UHS-I class of cards in our performance database.

In addition to raw performance and consistency, pricing is also an important aspect. This is particularly important in the casual user and semi-professional markets, where the value for money metric often trumps benchmark numbers. The table below presents the relevant data for the SanDisk Ultra microSDXC UHS-I 400GB uSD card and other similar ones that we have evaluated before. The cards are ordered by the $/GB metric.

uSD Cards - Pricing
Card Model Number Capacity (GB) Street Price (USD) Price per GB (USD/GB)
SanDisk Ultra microSDXC UHS-I 400GB SDSQUAR-400G-GN6MA 400 94 0.23
SanDisk Extreme microSDXC UHS I 128GB SDSQXAF-128G-GN6MA 128 39 0.30
PNY Elite microSDXC UHS I 512GB P-SDU512U190EL-GE 512 280 0.55
ADATA Premier ONE microSDXC UHS II 256GB AUSDX256GUII3CL10-C 256 224 0.88
FreeTail EVOKE Pro microSDXC UHS II 64GB FTUD064A10 64 56 0.88
Lexar 1800x 128GB LSDMI128CRBNA1800R 128 190 1.48
SanDisk Extreme PRO microSDXC UHS II 128GB SDSQXPJ-128G-GN6M3 128 200 1.56

The SanDisk Ultra card is not meant to be a benchmarks winner - rather, SanDisk wants to focus on the market segment which requires high capacity with minimum guaranteed performance numbers for usage in application scenarios (such as loading games in smartphones or even portable game consoles). The Ultra is an attractive card for content creators in the field who want to record a lot of content between imports to a bigger PC or network-connected mass storage device. It also targets users who can't afford the downtime / recording break that is inevitable during card swaps (when using smaller capacity cards). The PNY Elite (that targets a similar market segment) does edge it out with a slightly higher capacity (512GB vs. 400GB).

Due to its UHS-I rating, the SanDisk Ultra doesn't sport enough performance to consistently record videos with very high bitrates. However, it should be more than enough for content in the 150 Mbps range. With its A1 rating, it is also a good choice for expanding the storage capacity of smartphones and portable game consoles such as the Nintendo Switch.

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  • Guspaz - Thursday, December 13, 2018 - link

    I bought one for $80 ($0.20/GB) on Black Friday and stuck it in my Switch. It's fast enough that a faster card wouldn't impact game load speeds on the Switch, and it's a whole lot of capacity for a pretty cheap price.
  • CookieBin - Saturday, December 15, 2018 - link

    Exactly my use case. My 128gb card was almost full after a few Nintendo Switch titles... So I bought the 400gb for $80. I'd like to point out that the crystal disk benchmarks are largely USELESS without disclosing the queue depth... And on that point. Your likely to only have one active file transfer, so a QD of 1 is more reasonable than the default 8.... Same thing for threads.
  • PeachNCream - Thursday, December 13, 2018 - link

    I settled on the SanDisk 400GB card for my phone after looking at the much higher price per GB for a 512GB card. While there isn't quite as much room, the price was a lot better and I feel like I have enough breathing room for another year or so which is something my 256GB card was not up to providing. Speed isn't a significant factor except that it was a chore to copy ~215GB of data from my old card.

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