The resource monitor displays under QUTShero (h5.2.8.3359) for ZFS-ARC and free RAM are incorrect.
QNAP has hardcoded the values for arc_max and arc_min in hero.
→ arc_max is about 80% of the installed RAM
→ arc_min is about 20% of the installed RAM (for 64 GB, this is 11.71 GB)
→ The setting for usable ARC (40%, 50%,…) actually controls the usable ARC.
→ 50% of arc_max would correspond to an ARC of about 25 GB (50% of 80%). However, this value is not displayed anywhere.
The resource monitor only shows the usage of arc_min as ZFS-ARC. That’s why the maximum is reached at 11.71 GB.
The actual ARC usage in the range of 11.71 GB to 25 GB (50% ARC) is displayed as “free” RAM in the resource monitor.
+++++++++++++++++
I compared the values from the resource monitor with those from librenms.
Two VMs were running (Win+Linux-Mint), ARC set to 50%
hero resource monitor:
62.55 GB available
34.52 GB used (Allocated + ZFS ARC + buffer + cache)
26.89 GB free
librenms:
62.55 GB available
57 GB used
++++++++++++++++++++++
One VM was running (Win), ARC set to 70%
hero resource monitor:
62.55 GB available
29.31 GB used (Allocated + ZFS ARC + buffer + cache)
32.09 GB free
librenms:
62.55 GB available
52 GB used
When starting a second VM, you get the following error message
→ Not enough memory resources, only 6.69 GB free (according to the resource monitor, there should be 32.09 GB free)
Therefore, the displays of the resource monitor must be incorrect.
