SSK SD303 512GB USB flash drive
Here you will find a detailed speed, performance and benchmark test review. Tested was the USB flash drive SD303 with 512GB (SD303-512GB) from the brand SSK.
| Technical specifications (manufacturer information) | |
| Product image | 
|
| Manufacturer | SSK |
| Model number | SD303-512GB |
| Capacity | 512 GB (477 GiB) |
| pSLC cache | 128 GB approx. |
| Read speed | 1000 MB/s |
| Write speed | 1000 MB/s |
| Interface | USB 3.2 Gen 2x1 (10 Gbit/s) |
| Connector | USB Typ A+C |
| Controller | n/a |
Compare product Compared to the test winner*
We put the 512 GB SSK USB flash drive through a detailed test. You can find the test result / test report here:
AS SSD Benchmark
Standard performance test
The standard test was performed with a 1 GB file. A total score of 1025 points was achieved.
Copy performance test
A common everyday scenario is simulated here. Three test folders are created:
- ISO (folder with two large files)
- Program (folder with many small files)
- Game (folder with small and large files)
The three folders are copied using the Windows copy command (cache remains enabled). The real-world test from 15 January 2026 shows performance during simultaneous write and read operations. The lower the duration, the better.
| AS SSD Copy Benchmark | Transfer rate: | Duration: |
|---|---|---|
| ISO two large files |
619.76 MB/s |
1.73 s |
| Program typical program folder with many small files |
191.23 MB/s |
7.36 s |
| Game a game folder with small and large files |
436.09 MB/s |
3.17 s |
Compression performance test
Here, speed is measured depending on how compressible the data is.
CrystalDiskMark Benchmark
Similar to AS SSD, two sequential and two random performance tests are carried out here and the write and read speed (manufacturer: 1000 MB/s and 1000 MB/s) the SSK USB flash drive is determined.
| CDM | Read [MB/s] | Write [MB/s] |
|---|---|---|
| SEQ1M Q8T1 |
1,089.01 |
1,028.43 |
| SEQ1M Q1T1 |
1,028.50 |
975.84 |
| RND4K Q32T16 |
240.38 |
315.33 |
| RND4K Q1T1 |
35.86 |
84.10 |
IOPS (Input/Output operations per second)
| CDM | Read [IOPS] | Write [IOPS] |
|---|---|---|
| SEQ1M Q8T1 |
1,038.60 |
980.80 |
| SEQ1M Q1T1 |
980.90 |
930.60 |
| RND4K Q32T16 |
58,685.80 |
76,985.40 |
| RND4K Q1T1 |
8,754.20 |
20,531.30 |
Average latency
| CDM | Read [µs] | Write [µs] |
|---|---|---|
| SEQ1M Q8T1 |
7,694.07 |
8,136.31 |
| SEQ1M Q1T1 |
1,019.19 |
1,074.00 |
| RND4K Q32T16 |
8,707.26 |
6,642.23 |
| RND4K Q1T1 |
114.07 |
48.58 |
HD Tune Pro long-term test
A long-term test was performed to fully utilize the storage. You can see from when a possible cache is full and write performance drops. A test file of 200 GB was written to the medium. After approx. 128 GB, the cache was full and performance was throttled.
The test file could at least be read with an average read speed of 745 MB/s and written at 805 MB/s.
ATTO Disk Benchmark
Here, a 256 MB file is written to the 512 GB SSK USB flash drive multiple times. The I/O block size varies (from 512 bytes to 64 megabytes). The larger the blocks, the faster writing and reading usually becomes.
SSD-Z Benchmark
Similar to HD Tune, a 500 MB file is written to the 512 GB SSK USB flash drive here. The transfer data is displayed. The more consistent the line, the better. Unfortunately, the tool no longer works correctly from around 4,000 MB/s and no line is displayed (and sometimes incorrect min/max data is shown).
Power consumption
The following screenshot shows the USB flash drive's power consumption at idle (standby) and during a read operation followed by a write operation. The drive consumes approx. 0.54 watts at idle. Maximum consumption was approx. 0.95 watts.
You can find information about the test system at the bottom of the homepage.
As an Amazon Associate I earn from qualifying purchases.