Restoring a PFS from a backup

[Aleksej Lebedev]

Hi!

Recently my 5T hard drive broke. It contained among other things a 
master PFS that was backed up to a remote host.

I replaced broken hard drive, formatted it and run hammer mirror-copy 
from the remote pfs. After that I upgraded the freshly copied PFS to 
master
and now I can't set up the backup process again. The command "hammer 
mirror-stream" simply doesn't do anything.

Both my new master PFS and old backup seem to work OK and I can even 
mirror-stream from them to other places. But I can't mirror-stream from 
master to slave.
I checked sync-end-tid on both of them and noticed that for some reason 
the TID of my new master is a bit behind the one on my slave.

So I guess I somehow a few changes from my backup were not commited to 
my new harddrive. The problem is I already upgraded this PFS to master 
and even made some changes on it (just for testing, I don't mind loosing 
them).

I realize that I can easily delete the master PFS, re-mirror it again 
from my backup and make sure it has the same sync-end-tid before 
upgrading it to master, but I would like to avoid it because the PFS is 
very large.

My question: is it possible to roll-back a PFS (master or slave) a few 
transactions back?

I noticed that "hammer pfs-update" allows to simply change sync-end-tid, 
but since I don't understand what it is made for I am in doubt. 
Especially because the man page states "Manually modifying this field is 
dangerous and can result in a broken mirror."

Is there a way to roll-back a PFS or I have to re-mirror it from my 
backup again?

(I also now that I can do a local mirror-stream from my new master to 
separate PFS, stop it right before the end and then finish mirroring 
from my backup, but I it requires a lot of copying anyway, though local 
is better than remote, which I would like to avoid.)

-- 
Aleksej Lebedev