It doesn’t happen very often, but once in a while, I need a new USB flash drive. This time around, I was looking for something cheap, of reputable make and 128Gb capacity. Interestingly, looking around my local computer shop, the cheapest option was a SanDisk Ultra Dual Drive m3.0 for AU$42. This was a surprise since this is a special USB drive with a regular USB Type A and a micro B connector for on-the-go (OTG) use and it was a few dollars cheaper than a regular drive with just the normal Type A connector. As a result, I just had to get one!
As with most other SanDisk products, it’s packed inside a plastic bubble encapsulated by glossy coloured cardboard with a hanging ear. The unit is called a SanDisk Ultra Dual Drive m3.0 and seems to be a new revision of their previous Dual Drives. The unit advertises itself as a flash drive for “Android Smartphones” with up to 150MB/s read speed over USB 3.0. Otherwise, it makes no speed claims. It comes with a 5-year warranty, and is supported by their own free “SanDisk Memory Zone” app available on Google Play.
Splitting the card apart reveals a folded warranty guide, an electronic anti-steal (EAS) sticker and the sealed bubble the drive comes in.
The drive is a relatively small unit, only the size of the two connectors back-to-back, surrounded by a smoked grey plastic frame. The grey central portion is attached to the body of the drive, while the frame slides down to reveal each port (to prevent simultaneous dual-connection which may cause device damage). The capacity and serial number are etched on the top of the Type A connector, although the connector is a modified type with no holes on the top.
The grey plastic extends to one side to help slide the drive into the desired position. This is held by small detents in the outer ring portion, seen at the top of the image.
The opposite side provides a loop for a lanyard, not supplied.
A look from the underside shows that two dimples are provided on the Type A connector to improve retention in ports, however, they are not completely opened. This is because the integrated “chip” probably resides in the lower-half of the Type A connector shell.
We get a hint of this when we look at the blue USB 3.0 connector insert in the Type A plug. The plug has raised lips to retain the storage chip inside the drive and the connector insert appears to have been soldered to pads on the chip itself. This is necessary, as unlike USB 2.0 connectors, a functional USB 3.0 connector cannot be made solely from pads on a PCB due to the springy connectors for the USB 3.0 differential pairs.
The other side has the micro-B connector, along with cut-outs for the retention tangs. It’s quite obvious, but worth mentioning, that this connector will only provide USB 2.0 speeds in OTG operation.
This is what it looks like, extended for use with a computer.
This is what it looks like when extended for OTG operation with a phone or tablet device. Note the design includes a lengthened micro-B plug to ensure that it can plug into recessed ports and ensure that it can be used even if a phone case is in use.
As usual, the drive is pretty much plug-and-play when it comes to desktop and laptop computers, being just a regular USB Mass Storage Device.
In its default format, it is supplied in FAT32 for broadest compatibility, but will not support single files larger than 4Gb. The default format provides a total capacity of 114GiB (122,980,499,456 bytes), with some already used.
This is due to the inclusion of a copy of the Sandisk Memory Zone app as an .apk file and a Quick Start Guide PDF on the drive. This could be useful if you intend to use the app on an Android device, although the latest version can always be downloaded from Google Play and other file managers should be able to use it provided your device supports USB OTG storage.
Prior to commissioning any drives for data storage, I like to test them to determine their performance and to ensure they are performing correctly. Testing was done on my new Ryzen-based workstation using the on-board chipset hosted ports under Windows 10.
HDTune showed an average read speed of 171.4MB/s, well in excess of the 150MB/s claimed on the package, making this drive a fast reader especially considering its price.
Testing the write speed with HDTune shows an average write speed of 13.4MB/s, which is slightly disappointing. This only makes it about as fast as a low-end Class 10 microSD card.
Filling the whole drive with random data and verifying it took a very long time, even longer than expected than the write speeds benchmarked. Maybe the drive is sensitive to the data written, the block size or alignment. At least no data appeared to have been corrupted.
Because I made a small error in my test protocol, I did the HDTune tests above first, which wiped out the formatting on the drive. As a result, I discovered that the drive’s performance seems to heavily depend on the formatting of the drive.
FAT32 USB 3.0
From left to right, the ATTO results of the drive formatted as FAT32 in Windows 10, as FAT32 VFAT using mkdosfs v4, and as FAT32 VFAT unaligned with minimum reserved sectors using mkdosfs v4.
The Windows 10 FAT32 alignment is at 2048 sectors and it seems to offer peak speeds of 184.5MB/s read and 16.4MB/s write. Going with VFAT pushes this to 184.7MB/s read and 21.4MB/s write. The most space-greedy VFAT format results in 184.7MB/s read and 16.4MB/s write. As a result, it seems mkdosfs v4 gives the best speed in VFAT mode with default settings.
FAT32 USB 2.0
Repeating the same with the drive connected as USB 2.0 resulted in the Windows 10 FAT32 formatted drive reporting 39.9MB/s read and 6.3MB/s write, the FAT32 VFAT drive reporting 39.6MB/s read and 24.1MB/s write and the maximum FAT32 VFAT unaligned drive reporting 39.7MB/s read and 6.2MB/s write. As a result, it seems the drive’s performance suffers in USB 2.0 mode especially when it is operated outside of its preferred alignment.
NTFS USB 2.0 and 3.0
With Windows 10 formatting the drive as NTFS, it doesn’t seem to exhibit any negative effects despite the partition starting at sector 2048. In USB 3.0, it offers a peak read of 180.9MB/s and a peak write of 21.5MB/s. In USB 2.0, this reduces to 39.9MB/s read and 24.0MB/s write.
exFAT USB 2.0 and 3.0
Using Windows 10 to format as exFAT doesn’t seem to cause any alignment issues despite having a partition start at sector 2048. In USB 3.0, it offers a peak speed of 178.9MB/s read and 21.5MB/s write. In USB 2.0, this reduces to 39.9MB/s read and 24.2MB/s write.
Luckily, before publishing, I purchased another fresh sample of the drive. I determined that the drive is partitioned as MBR FAT32 with an alignment of 32 sectors.
The performance from ATTO over USB 3.0 shows that the second untested/unworn drive offers only marginally higher performance than the FAT32 VFAT example above, but that’s not unexpected given the fresh state of that drive.
The drive is capable of peak speeds of about 180MB/s read and 22.5MB/s write with full performance at around 256KB accesses. As a result, it seems that the mkdosfs v4 results and the Windows 10 format to NTFS and exFAT are all fairly close to factory for performance, whereas the Windows 10 format to FAT32 reduces performance significantly and could reduce the lifetime of the drive through unaligned writes.
CrystalDiskMark shows the performance of the drive as FAT32 (formatted by Windows) and FAT32 VFAT (formatted by mkdosfs v4) on the right. It seems to suggest the sequential performance can reach up to 182.8MB/s read and 21.39MB/s write, but suffers heavily under small block accesses. It also seems to suffer under multiple queue access as well.
I tested the drive in FAT32 (formatted by Windows) and FAT32 VFAT (formatted by mkdosfs v4) using H2testW and it passed both tests. Read speeds did not change between either run, registering around 155MB/s (more than claimed on the package), although write speeds increased for the VFAT drive to 14.7MB/s.
I tested it with my normal daily-use phone, a Xiaomi Mi Max running Xiaomi.eu ROM.
When plugged in, the drive is immediately detected and ready for use.
It turns up in the storage section under settings and can be accessed through the file manager. As it turns out, it works if formatted in FAT32 or exFAT, but does not work if formatted in NTFS.
In the case of NTFS format, the following prompt appears when plugged in.
I tested the speed using A1 SD Bench, although I don’t find the figures highly reliable.
FAT32 in VFAT format
I was looking for an inexpensive 128Gb USB 3.0 drive and the Sandisk Dual Drive m3.0 was the answer. The drive offers very fast read performance especially over USB 3.0 for a drive of this price range, but the write speed was very average (up to 22.5MB/s peak, but around 15-18MB/s sustained) and of the sort you might expect from a low-end Class 10 SD card. Even a Samsung EVO+ microSD card would run rings around it in this regard. This is not unexpected considering that the drive is cheaper than most regular plain USB 3.0 drives.
The differentiator, however, is the presence of the USB microB port for USB OTG usage. This allows you to use the drive with supported devices to copy files to and from the device for backup or expanded storage. While I won’t recommend “hanging” the drive off the port for extended periods as an accidental knock might break something, it has come in handy for a quick file transfer (e.g. instead of uploading to the cloud or getting a USB cable to plug the phone into the computer directly). However, this all depends on your device and whether it supports OTG storage devices. Filesystem support also varies from device to device. You can test it out with any ordinary USB key and a USB OTG adapter.
As a result, it seems a decent buy even if you’re just interested in using it as a regular USB key instead of a dual drive. But whatever you do, avoid reformatting the drive if you wish to retain its full performance. If you must, it seems Windows 10’s default 1MB/2048 sector alignment works just fine for NTFS and exFAT, but not so well for FAT32. mkdosfs v4 in Linux seems to do a better job for FAT32.