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SanDisk microSD UHS-II USB 3.0 Reader SDDR-339 Review

SanDisk microSD UHS-II SD Reader USB 3.0 SDDR-339


The SanDisk microSD UHS-II Reader (SDDR-339) is included with SanDisk Extreme Pro UHS-II MicroSD cards. It offers high-speed USB 3.0 compatibility for maximum transfer speed. It is compatible with microSD, microSDHC and microSDXC cards and supports both UHS-I and UHS-II. Few card readers have the separate row of pins necessary to connect using the UHS-II interface; in many readers UHS-II cards will only operate in UHS-I mode at lower speed. Having a dedicated UHS-II microSD reader is necessary to take advantage of the additional speed offered by UHS-II microSD cards.

The external case of the SanDisk microSD UHS-II Reader is black plastic with a brushed metal insert on the top. The end of the reader is slanted and has a single microSD slot. A small hole below the microSD slot will accommodate a string to attach it to a keychain. There is no card access light.

SanDisk microSD UHS-II Reader bottom

When a microSD card is inserted into the reader only about 2.5mm of the card remains outside, just enough for a fingernail to catch on the small raised portion at the end of the microSD card. The reader measures 1 5/16 x 3/4 x 1/4 inches (33 x 19 x 6mm). It is practically the same overall size as the microSD card readers included with Lexar microSD cards.


The SanDisk microSD UHS-II Reader reached up to 242.0 MB/s sequential read speed in benchmark tests. A read speed of 239.4 MB/s was reached using the SanDisk Extreme Pro UHS-II 64GB microSDXC card. The highest sequential write speed using UHS-II cards was measured at 211.6 MB/s using the Lexar Professional 1800x 32GB microSD UHS-II card. Using UHS-I microSD cards, the reader offered speeds up to 94.3 MB/s sequential read and 88.2 MB/s sequential write.

Comparing several microSD in the SanDisk microSD UHS-II reader with other micro UHS-II readers (including size SD UHS-II readers with SD to microSD UHS-II adapters), the performance of this SanDisk microSD reader is on par with most. Only two Lexar readers, the Professional Workflow SR2 and LRWM04U-7000, offered significantly higher read speeds.

Few readers support UHS-II microSD cards, making a dedicated reader a practical necessity to take advantage of the additional speed offered by UHS-II. SanDisk probably had this in mind when the decision to include the reader with the Extreme Pro UHS-II microSD cards was made.

Reader: SanDisk microSD UHS-II USB 3.0 Reader
Benchmark: CrystalDiskMark 3.0.3 x64
Program settings: 1000 MB, 5 passes, random test data
Operating system: Windows 8.1 Pro
Motherboard: Gigabyte GA-Z77X-UD3H
Processor: Intel Core i7-3770K @ 4.40GHz
RAM: 32GB DDR3 1600

SanDisk microSD UHS-II USB 3.0 Reader
Card Benchmarks
Lexar Professional 1800x microSD UHS-II 32GB242.026211.556
SanDisk Extreme Pro UHS-II 275MB/s microSDXC 64GB239.374105.586
Lexar Professional 1000x microSD UHS-II 32GB151.74852.836
SanDisk Extreme Plus 95/90 MB/s microSD 64GB94.25488.197
SanDisk Extreme 90MB/s microSDXC 128GB93.86664.216
SanDisk Extreme Plus 95/90 MB/s microSD 32GB93.81688.079
SanDisk Extreme Pro 95MB/s microSDXC 64GB93.68187.681
SanDisk Extreme 90MB/s microSDHC 32GB93.66548.962
SanDisk Extreme Pro 95MB/s microSDHC 32GB93.65687.200
SanDisk Extreme Plus 80MB/s microSD 32GB93.63165.307
Transcend 633x microSDHC 32GB93.24883.900
Samsung PRO Select microSDXC 64GB93.19884.122
Kingston U3 (90/80) microSD 64GB93.05883.685
PNY Pro Elite microSDXC 64GB93.04184.823
Patriot EP PRO microSDXC 64GB93.00084.115
Kingston U3 (90/80) microSD 32GB92.84483.639
Patriot EP Series microSDXC 64GB92.80386.480
PNY Elite-X microSDHC 32GB92.73775.863
Transcend Ultimate 633x microSD 64GB92.67184.508
Samsung EVO Select microSDXC 256GB92.60683.960
Samsung EVO Select microSDXC 64GB92.57325.156
PNY Turbo Performance microSDXC 64GB92.53257.037
Samsung PRO Plus microSDXC 64GB92.46784.358
Samsung PRO microSDXC 64GB92.44378.275
PNY Elite microSDXC 128GB92.40228.449
PNY Elite-X microSDXC 64GB92.29673.776
PNY Turbo Performance U3 microSD 32GB92.28054.537
SanDisk Extreme 90MB/s microSDXC 64GB91.67543.462
SanDisk Ultra 90MB/s microSD 200GB90.56620.682
Samsung PRO Plus microSDXC 128GB90.13083.532
Samsung PRO Select microSDXC 128GB89.96083.181
Lexar Professional 633x microSDXC 200GB88.60734.726
SanDisk Ultra 80MB/s microSD 64GB84.91220.532
Lexar Professional 633x microSDXC 128GB84.51522.525
Samsung EVO Plus 128GB microSDXC83.57922.630
SanDisk Ultra (80MB/s) microSD 32GB82.57817.173
Samsung EVO Select microSDXC 128GB81.44922.432
SanDisk Extreme U3 microSD 32GB74.62653.997
PNY Elite microSDXC 64GB69.18624.580
Lexar Professional 633x microSDXC 64GB68.77319.024
SanDisk Extreme U3 microSD 64GB68.05456.044
SanDisk Ultra microSD 64GB46.44015.827
SanDisk Ultra microSD 32GB46.37514.698
Samsung EVO microSDXC 64GB46.35223.466
Samsung EVO microSD 32GB46.33424.529
SanDisk Ultra 80MB/s microSD 128GB35.02029.359

The SanDisk microSD UHS-II Reader (SDDR-339) is not currently available for purchase separately. It is included with SanDisk Extreme Pro UHS-II microSD cards such as the Extreme Pro 275MB/s 64GB microSDXC UHS-II card.