Cleanup of slave PFSes

[Marco Righele]

Greetings,

I have trouble understanding how daily cleanup jobs interact with slave 
PFSes being updated with
hammer mirror-stream.

I have a hammer volume (ROOT) of a size of about 150GB with a number of 
PFSes on it.
All PFSes are mirrored to another volume (BACKUP) of the same size, to 
slave PFSes with the same name.
BACKUP is mounted on /backup, so for example /pfs/data is mirrored to 
/backup/pfs/data.

I noticed that while the nightly job runs hammer cleanup just on the 
PFSes on the ROOT volume, not on BACKUP,and in fact the free space on 
BACKUP keeps getting lower.
Manually running `hammer cleanup` on the slaves recovers only a portion 
of the space, not all. Is there a reason for this behaviour, or is there 
something wrong in my configuration ?

Anyway, how can I enable the cleanup of PFSes other than in the ROOT 
volume ? Is there a reason why this is not done by default ? Just 
pointers to documentation would suffice (I checked hammer(8), but I 
didn't find anything relevant).

Thanks in advance,
Marco