There are some things in vardir which can be removed before you archive it. They are either copies of files from elsewhere, or just useless.
My probably incomplete and possibly incorrect list currently is:

• std_data
• plugins (<- for source builds)
• run
• tmp
• install.db
• mysqld.N (<- these look important, but in reality if the test failed, they would be under log/testname/, not in vardir directly)

One example of required file is:

mysql-test/var/log/mariabackup.huge_lsn

Since this can be quite large, we probably need to define a separate service that uploads the files to make them available. Potential flow:

1. Buildbot creates the archive and stores it on the worker side.
2. A separate service uploads the archives to be available to download.
3. On the builder page, there needs to be a link to the appropriate archive.

Problems: since the upload will not be made during the actual build step, there will be a timeframe where the link to download the archive does not work.

vladbogo I suggest we try to skip the 2/, since all workers are connected to BB master (wireguard), it should not be too difficult to make this available from ci.mariadb.org (or something else) with a nginx reverse proxy (or haproxy).

So that would be:
1. Buildbot creates the archive and stores it on the worker side;
2. On the builder page, there needs to be a link to the appropriate archive;
3. Define retention of such archive (warning not all workers have the same storage capacity).