## 6 Performance Evaluation
### Directory Deactivation Experiment  
In the first scenario, the directory deactivation experiment performs periodic file access operations during the first 3 days and performs no file access during the second 3 days. That is, the first 3 days are the directory activation period, and the last 3 days are the directory deactivation period. Starting the experiment with the synchronization directory empty, the file access operation during the first directory activation period repeats two operations: adding new files and updating existing files. The cycle for adding new files is 5 h and the cycle for updating existing files is 2 h. To add new files, we created 10 test files in the temporary directory in advance and copied them one by one to the synchronization directory at each addition cycle. We updated existing files one by one at every update cycle, starting with the files newly added to the synchronization directory. The file update method proceeds differently depending on the file mode. Updating a local mode file overwrites the same test file in the temporary directory by copying it back to the synchronization directory. In case of an online mode file, the update operation first changes the file to the local mode. In this experiment, we measured the local storage usage ratio and the file access delay during the directory transition from active to inactive state. To this end, whenever a file access (new addition or update) operation is performed during the experiment period, we recorded the current local storage usage and the file mode of the accessed file. We record the mode of the file we accessed to get the cost of accessing the file. When accessing a local mode file, there is no download cost, whereas when accessing an online mode file, there is a cost to download the entire file from the server to change it to the local mode. In this experiment, since the file sizes are all the same, the file access cost was measured by the number of times the online mode file was accessed, not the actual download time. We conducted directory deactivation experiments under the same conditions mentioned above for the manual file mode change mechanism and the proposed active file mode change mechanism. In the case of the active file mode change mechanism, to observe the effect of changing parameters on the local storage usage ratio and file access cost, we conducted the experiment by changing three thresholds, including elapsed time since last access threshold (_DSLAT_), online mode threshold (_OMT_), and used storage ratio threshold (_USRT_). The local mode threshold (_LMT_) must be greater than or equal to the online mode threshold (_OMT_). In this experiment, we set the _LMT_ and the _OMT_ to the same value. During the entire experimental period of the directory deactivation scenario, we analyzed only the local storage usage changes, not the file access costs, as clients mostly accessed only the local mode files. Figure 8 shows the change in local storage usage when the manual file mode change mechanism is applied to the directory deactivation scenario. Starting with the directory empty, we can see that the local storage increases for each new addition of 1 MB-sized test file over the first 3 days. After the 3 rd day of the experiment (after about 68 h), even during the period of no file access, the storage usage continues to maintain 100% of 10 MB. Because the manual file mode change mechanism keeps the original mode unless the user manually changes the file mode, a low directory activation ratio without file access is a waste of local storage. \begin{table}
\begin{tabular}{c c c} \hline  & **Server** & **Client** \\ \hline OS & macOS Monterey & Windows 11 Pro \\ \hline CPU & 2.4 GHz, Intel Core i5 & 2.3 GHz, Intel Core i7 \\ \hline Memory & 16 GB & 16 GB \\ \hline Storage & SSD 512 GB & SSD 1 TB \\ \hline \end{tabular}
\end{table} 
Table 3: Device Specifications of Synchronization Server and Client.