## 6 Performance Evaluation
### Directory Activation Experiment
During the directory deactivation period, the larger the _DSLAT_ value, the longer the files remain active, so the initial local mode state (storage usage of 6 MB) is also maintained. As the _DSLAT_ value decreases, the directory activation ratio decreases quickly, and the active file mode change mechanism starts early to change the local mode files back to the online mode. For example, when the _DSLAT_ is 24 h (dslat-24), storage usage decreases after 63 h from the start of the experiment, and when the _DSLAT_ is 6 h (dslat-6), storage usage decreases after 21 h. Since the experiment performed the change to the online mode within the range where the storage usage does not go lower than the _USRT_ default value of 0.5 (50%), the storage usage is kept at a minimum of 5 MB. When the directory activation period is reached, the file access operation begins. As the online mode file is accessed, the local storage usage gradually increases as it changes to the local mode. The _DSLAT_ value of the directory activation period affects when storage usage starts to increase. If the _DSLAT_ value is large, the chance of changing to the online mode is less because the local mode file maintains an active state for a long time, and the online mode files are accessed one by one and change to the local mode, increasing storage usage. For example, if the _DSLAT_ is 36 h (dslat-36), we can see that the local storage usage continues to increase after 84 h. If the _DSLAT_ value is small, the local mode files that are not accessed are quickly inactive, these files are changed to the online mode, and the local storage usage is reduced. On the other hand, when the online mode files are accessed, they change to the local mode and increase the local storage usage. As the local mode file and the online mode file change the mode together, the local storage usage is maintained at a certain level. For example, if the _DSLAT_ is 6 h and 12 h (dslat-6, dslat-12), the local storage usage keeps repeating between 5 MB and 6 MB. As the _DSLAT_ value increases, if the local mode change rate becomes larger than the online mode change rate, the local storage usage starts to increase. In Figure 13, in terms of local storage usage, the active file mode change mechanism continues to use more than 5 MB of storage during the experimental period, but the increase  
Figure 13: Change of local storage usage of active file mode change mechanism according to _DSLAT_ in directory activation scenario. (**a**) dslat-6. (**b**) dslat-12. (**c**) dslat-18. (**d**) dslat-24. (**e**) dslat-30. (**f**) dslat-36. point varies according to the _DSLAT_ value. In the manual file mode change mechanism, the storage usage is minimal during the directory deactivation period, and the usage increases linearly as soon as the activation period starts. Since it is difficult to determine which mechanism is better based on the local storage usage alone, we also compared the number of online mode file accesses in terms of file access cost as shown in Figure 14. The manual file mode change mechanism has 10 online mode file accesses, which means that all 10 test files accessed for the first time were in the online mode. The active file mode change mechanism shows a decrease in the number of online mode file accesses as the _DSLAT_ value increases. This is because the larger the _DSLAT_ value, the more files are active, and the probability that such files are changed to the local mode before access increases. If the _DSLAT_ value is small, the number of files in inactive state increases, and the probability that such files are changed to the online mode increases, and the number of online mode file accesses also increases. In other words, if the _DSLAT_ value is small, the local storage usage can be maintained at a certain level, but the file access cost increases accordingly. Figure 15 shows the change in the local storage usage according to the local mode threshold (_LMT_). Since the _LMTs_ from 0 to 0.4 have the same results, we showed the measured values from 0.4.