test btrfs scrubbing/get system's total capacity

[ST <smntov@gmail.com>]

Hello,

1. is there a tool that I can use to test btrfs scrubbing? Namely I need
to "damage" a file, i.e. change it without changing its meta
information, so I can see how scrubbing performs... Is there something
like this?


2. I want to use Ansible to set btrfs quota on a /home subvolume as say
0.8*TotalCapacityOfRoot and then assign to it individual users'
subvolumes with certain (smaller) quatos.
2.1 Is it OK to rely on ansible_facts? Does it has correct information
about btrfs-based "/" total capacity?
2.2 If not, is there a raw command to get TotalCapacityOfRoot in -TB so
I can set it? Is there something like btrfs filesystem usage / -t
--device_size? to get only the total Device Size information?

Thank you!
ST