Restoring a PFS from a backup

[Tim Darby]

This is an issue I've reported: http://bugs.dragonflybsd.org/issues/2915

My way around this is to create the new master and use cpdup to copy the
PFS slave to it.

Tim


On Mon, Oct 29, 2018 at 6:22 AM Aleksej Lebedev <root at zta.lk> wrote:

> 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
>
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