Restoring a PFS from a backup

[Aleksej Lebedev]

On 2018-10-29 15:12, Tim Darby wrote:

> 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

Hi, Tim.

Thanks for your reply.
Your problem does look similar to mine. But I now think it might not be 
a bug: latest transactions might not be commited.
Reading through the manual once more I noticed there is a command 
"hammer synctid" which syncs the PFS and gives you the TID that you 
might use to check that mirror-copy/stream reached it.

I will experiment with it a bit more and let you know if the problem 
resolves.

--
Aleksej Lebedev

> 
> 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