One of Silverstack’s key features is the fast, checksum-verified backup to multiple destinations. This means that you can copy media files from camera media to different external volumes with a verification process that ensures the completeness and integrity of your files on each destination.
The copy process is split into two phases: The “Copy” phase and the “Verify” phase. Figure 1 illustrates these two phases:
Figure 1: The two phases of the copy process
In the Copy phase the reading speed from the source and the writing speed to each destination is the same. When the Copy phase is finished, the file verification takes place. The writing speed drops to zero and the reading speed increases, as Silverstack is reading all files again from the copy destinations as well as from the source (see Figure 2). You can monitor the transfer rates in Silverstack’s job view and in macOS’s Activity Monitor application.
- Figure 2: Writing speed (red) and reading speed (green) during Copy and Verify phase.
The “Combined Speed” as shown in Silverstack’s job view by default may be lower than the maximum transfer rates (or the rates that can be seen when copying with Finder) due to the additional verification process. This process ensures that the files you have copied are exactly the same as in the source.
You can skip the verify process in the Offload and Backup wizards, but we strongly advise to use verification in a real production scenario.
The maximum copy speed, that Silverstack performs, is determined by the hardware setup you are using. The slowest of the components will define the system’s final speed. The articles “Factors for data-transfer performance” and “Analyzing and improving data-transfer performance” explain in detail all the improvements and hardware specifications that can modify the copy process performance.
It is possible to modify Silverstack’s behaviour concerning multiple tasks in the application preferences, as described in the article “Tweaking copy performance“.