## 6 Performance Evaluation
### Directory Activation Experiment
As in Figure 13 (_DSLAT_), because the active file mode change mechanism performs the local mode change at the start of the directory activation experiment, the storage usage in Figure 15 starts at 6 MB that exceeds 50% of the total capacity (because the _USRT_ default is 0.5). During the initial directory deactivation period, even if files are changed to the online mode, the local storage usage is maintained at a minimum of 5 MB. Just as the local storage usage graphs according to the _DSLAT_ and the _OMT_ were similar in the first directory deactivation scenario, the graphs according to the _DSLAT_ and the _LMT_ are similar in the directory activation experiment. During the initial directory deactivation period, the higher the _LMT_ value, the higher the reference value for the active file mode change mechanism to determine that the directory is activated. Therefore, the online mode change occurs early, and then the storage usage decreases. For example, when the _LMT_ value is 1 (lmt-1.0), the storage usage decreased after 42 h of the experiment start. In the case of a smaller _LMT_, the usage decreases later. During the latter period of directory activation, file access operations are initiated. At this time, the larger the _LMT_ value, the stronger the tendency of the active file mode change mechanism to keep the files in the online mode, and the storage usage does not increase well. This is because the rate of change to the local mode by file access and the rate of change to the online mode by the  
Figure 14: Change of the number of online mode file accesses according to _DSLAT_ in directory activation scenario. active file mode change mechanism are similar. As the _LMT_ becomes smaller, the storage usage tends to increase early because the active file mode change mechanism weakens the tendency for files to change to the online mode. For example, if the _LMT_ is 0.4 (Imt-0.4), the storage usage increases after 91 h. whereas if the _LMT_ is 0.7 (Imt-0.7), the storage usage starts to increase after 126 h.  
As shown in Figure 15, in terms of the local storage usage only, the larger the _LMT_ value, the better it seems, because it maintains a relatively low storage usage, and it is difficult to judge which method is better compared to the manual file mode change mechanism. However, as shown in Figure 16, the results may be different when looking at the file access cost. If the _LMT_ value is large, the local storage usage decreases because the number of online mode files is relatively large. However, as the number of online mode files increases, the probability that the accessed file is in the online mode also increases, and the access cost increases. The manual file mode change mechanism is good in terms of the local storage usage but results in high file access cost. The active file mode change mechanism allows us to choose the more important factor between the local storage usage and file access cost and adjust the threshold accordingly. If the user wants to reduce the local storage usage and delay its increase as much as possible, he/she can increase the _LMT_ value. If the user has many large files and wants to quickly change to the local mode to reduce file access costs, he/she can reduce the _LMT_ value. Figure 15: Change of local storage usage of active file mode change mechanism according to _LMT_ in directory activation scenario. (**a**) Imt-0–Imt-0.4. (**b**) Imt-0.5. (**c**) Imt-0.6. (**d**) Imt-0.7. (**e**) Imt-0.8. (**f**) Imt-0.9. (**g**) Imt-1.0. Figure 17 shows the change in the local storage usage of the active file mode change mechanism according to the various _USRT_ values in the directory activation experiment. _USRT_ is the lower or upper bound reference value for local storage change when the active file mode change mechanism changes a file to the online mode or local mode. For example, if the _USRT_ value is 1 (usrt-1.0) during directory deactivation period, the active file mode change mechanism can use 100% of local storage when changing to the local mode.