Brave ignores --disk-cache-dir flag, caches Torrent downloads always on primary harddisk

[crcdng]

Description

Brave always caches Torrent downloads on primary harddisk, ignores --disk-cache-dir flag

Steps to Reproduce

1. Start Brave on a machine with a primary HD and a secondary HD, e.g. a USB connected drive
2. Set Download location in "Settings -> Additional Settings -> Downloads -> Location" to secondary HD
3. Start a (large) download on built-in Web Torrent. A large download makes the problem visible.

Intermediate Result: Brave fills up the primary HD

1. Start Brave with flag --disk-cache-dir pointing to secondary HD
2. E.g. on a Mac run in Terminal '"/Applications/Brave Browser.app/Contents/MacOS/Brave Browser" --disk-cache-dir=/Volumes/secondary/cache'
3. Start large Download on built-in Web Torrent

Actual result:

Result: Brave initiates a cache on the secondary HD in the specified location but still fills up the primary HD

Remark: The space on primary HD is released after closing Brave.

Expected result:

Result: Brave should not fill up the primary HD. The reason to use a secondary HD is limited space on the primary HD.

Reproduces how often:

Always.

Brave version (brave://version info)

Brave | 1.19.88 Chromium: 88.0.4324.96 (Official Build) (x86_64)
Revision | 68dba2d8a0b149a1d3afac56fa74648032bcf46b-refs/branch-heads/4324@{#1784}
OS | macOS Version 11.2 (Build 20D64)

[diracdeltas]

cc @yrliou @feross

[feross]

This issue is a bit odd because WebTorrent currently uses an in-memory only downloading strategy.

@i3games Perhaps what is happening is that your RAM is being used up and the operating system is moving other memory to disk in a swap file. Can you check your RAM utilization when using WebTorrent and confirm if this is what you see?

If it's using your swap file as I suspect, then this issue will be resolved when we switch to a filesystem based store which will obey the Brave --disk-cache-dir flag. See #5563 issue.