Secure Digital (SD) Flash Cards Performance
Due to the recent advances in the NAND flash memory technology, the market of Secure Digital (SD) flash cards become saturated with many options at very competitive prices. The problem is how to choose from all the available options especially when almost all vendors SD flash cards are promoting their products with very similar performance numbers making it difficult for an average user to select an appropriate option.
Normally, Secure Digital (SD) flash cards are used in digital cameras to store still images and video files, but recently some hardware vendors started to sell SD-to-SATA adapters with built-in hardware RAID capabilities making it possible to install a number of SD cards into an adapter and then connect the adapter to a computer using a regular SATA cable allowing one access the installed SD cards as a single SSD disk.
Theoretically, an SD-to-SATA adapter with built-in RAID-0 capabilities should evenly distribute all I/O operations across all the installed SD cards and therefore the resulting performance should linearly increase according to the number of used SD cards. Some vendors of SD cards are stating that their products can reach up to 95 MB/Sec of disk transfer rate and therefore 4 such SD cards installed into an SD-to-SATA adapter with built-in RAID-0 capabilities should deliver up to 380 MB/Sec, 6 SD cards should deliver up to 570 MB/Sec, etc. For example, here is a picture of an SD-to-SATA adapter allowing one to connect up to 10 micro-SD flash cards:
On paper, the option to build a fast SSD disk using a number of cheap SD cards looks very tempting, but SD cards are designed for a very specific task of storing still images and video files, which are relatively large, and therefore it is not clear how good are SD flash cards in normal usage scenarios with different types of file I/O operations and modern file systems such as NTFS and exFAT. Before rushing to purchase a bunch of SD cards and an SD-to-SATA adapter, let's check how fast are modern SD cards in real-life disk usage scenarios with different types of files and then estimate how fast may be an SSD disk based on a number of SD cards installed into an SD-to-SATA adapter.
In order to get a better understanding about what to expect from different types of SD flash cards, we have tested the following Secure Digital (SD) flash cards:
In order to measure the performance of the selected SD flash cards, we have performed the following tests:
All tests were performed using DiskBoss v7.7.14 (64-Bit), which is capable of performing different types of file copy, file synchronization, disk space analysis, file classification, duplicate files search, file search and file delete operations. All the tested SD flash cards were benchmarked using exactly the same set of files, in the same order and on the same hardware platform. In order to be able to understand how the file system affects the performance of the tested SD flash cards, each SD card was benchmarked 3 times and each time the SD card was reformatted using one of the following file systems: FAT32, exFAT and NTFS.
In addition, during each benchmark, the benchmarked SD flash card was monitored using the SysGauge performance monitoring utility configured to monitor the disk transfer rate, disk transfer IOPS, file system data IOPS and file system control IOPS. For each benchmark, the SysGauge performance monitoring utility saved a graphical PDF report including the average, minimum and maximum performance and also a line chart showing how each SD flash card behaved during the entire benchmark.
In order to easily compare different types of disk performance results, all results were normalized and a normalized disk performance index has been calculated for each tested SD card. As it is clear from the disk performance results, the SanDisk Extreme SD flash card delivers significantly better disk performance in almost all types of performance tests.
For example, when copying large files the SanDisk Extreme SD flash card can reach up to 63.6 MB/Sec when formatted using the NTFS file system and up to 63.2 MB/Sec with the exFAT file system. On the other hand, with the standard FAT32 file system the same SD card delivers significantly lower performance results managing to reach only 38.4 MB/Sec. In the same test, the Transcend Ultimate SD card managed to reach up to 56.5 MB/Sec with the exFAT file system and 53.1 MB/Sec when formatted using the NTFS file system.
When copying medium-sized files, the SanDisk Extreme SD card delivers up to 54.2 MB/Sec with the exFAT file system and 51.1 MB/Sec when formatted using the NTFS file system. In the same test, Transcend Ultimate SD card managed to reach up to 45.3 MB/Sec with the exFAT file system and 39.3 MB/Sec when formatted using the NTFS file system. On the other hand, the tested Kingston SD card managed to reach up to 38.2 MB/Sec with the exFAT file system and just 26.7 MB/Sec when formatted using the NTFS file system.
As expected, the small-files performance is less promising for all types of SD cards. For example, the SanDisk Extreme SD card managed to reach up to 11.7 MB/Sec with the exFAT file system and up to 10.3 MB/Sec when formatted using the NTFS file system. On the other hand, with the standard FAT32 file system, the same SD card managed to reach just 6.1 MB/Sec. Other tested SD cards managed to deliver approximately 5-7 MB/Sec, while some got even less than 1 MB/Sec.
The performance of disk space analysis, file classification and directory scanning operations is more consistent and largely depends on the selected file system. All the tested SD cards managed to reach approximately 3,000 Files/Sec with the NTFS and exFAT file systems, while the FAT32 file system consistently delivered significantly slower results and managed to reach approximately 1,250 Files/Sec, which is not good enough when compared to 50,000-80,000 Files/Sec normally delivered by a regular SSD disk.
The performance of the file delete operations is really disappointing and it also varies greatly between different types of SD cards. The SanDisk Extreme managed to reach up to 352 Files/Sec with the NTFS file system, the Transcend SD card managed to reach up to 264 Files/Sec with the NTFS file system while all the rest benchmarked SD flash cards delivered less than 200 Files/Sec, which is very slow when compared to 10,000-20,000 Files/Sec normally delivered by a regular SSD disk.
As it was expected, Secure Digital (SD) flash cards are optimized to store a relatively small number of large files and in normal usage scenarios SD flash cards deliver disappointing performance results especially when copying large numbers of small files, analyzing large numbers of files and deleting large numbers of files. Even when taking into account potential performance improvements that can be provided by an SD-to-SATA adapter with built-in RAID-0 capabilities, the resulting disk performance in normal usage scenarios is expected to be slower than a cheap SSD disk of the same capacity.
* This review was prepared for information purposes only and we strongly recommend to test the performance of DiskBoss file management operations on your specific hardware platform and with your specific data sets.