Item that returns the remaining mounted space without concern for reserved space.

[zabbix_mouse_123]

Zabbix Server Version: 7.0.17

As the title suggests, I am trying to create an item that determines the free space of the mounted file systems on some Ubuntu servers, each with a couple of mounted file systems.

As it stands currently, the hosts (my ubuntu servers) are inheriting a template, with a discovery rule named 'mounted filesystem discovery' whose Key=vfs.fs.discovery.
Furthermore, this template has 4 item prototypes, whose keys are:
vfs.fs.inode[{#FSNAME},pfree]
vfs.fs.size[{#FSNAME},pused]
vfs.fs.size[{#FSNAME},total]
vfs.fs.size[{#FSNAME},used]

These items 'work' and the mounts are discovered and read on my hosts.

According to the 7.0 docs, for vfs.fs.size:
"The reserved space of a file system is taken into account and not included when using the free mode.". I want the opposite.

I confirmed this fact, when trying 'vfs.fs.size[{#FSNAME},free' key as an Item prototype, I still am about 5% * total drive space less than how much actual free space I have.

I tried creating an item prototype that just subtracts total space - used space as an item prototype, but I couldn't figure it out. I can think of a few really ugly work-arounds, but there has got to be a nice way of doing this that I do not currently know.

Thanks!

[zabbix_mouse_123]

I was able to make it work using a calculated item prototype, it looks like:
Key: filesystem.true_available_space[{#FSNAME}]
Formula: last(//vfs.fs.size[{#FSNAME},total]) - last(//vfs.fs.size[{#FSNAME},used])