Re: trouble mounting btrfs filesystem....

[Andrei Borzenkov <arvidjaar@gmail.com>]

14.08.2018 18:16, Hans van Kranenburg пишет:
> On 08/14/2018 03:00 PM, Dmitrii Tcvetkov wrote:
>>> Scott E. Blomquist writes:
>>>  > Hi All,
>>>  > 
>>>  > [...]
>>
>> I'm not a dev, just user.
>> btrfs-zero-log is for very specific case[1], not for transid errors.
>> Transid errors mean that some metadata writes are missing, if
>> they prevent you from mounting filesystem it's pretty much fatal. If
>> btrfs could recover metadata from good copy it'd have done that.
>>
>> "wanted 2159304 found 2159295" means that some metadata is stale by 
>> 9 commits. You could try to mount it with "ro,usebackuproot" mount
>> options as readonly mount is less strict. If that works you can try
>> "usebackuproot" without ro option. But 9 commits is probably too much
>> and there isn't enough data to rollback so far.
> 
> Keep in mind that a successful mount with usebackuproot does not mean
> you're looking at a consistent filesystem. After each transaction
> commit, disk space that is no longer referenced is immediately freed for
> reuse.
> 

With all respect - in this case btrfs should not even pretend it can do
"usebackuproot". What this option is for then?

> So, even if you can mount with usebackuproot, you have to hope that none
> of the metadata blocks that were used back then have been overwritten
> already, even the ones in distant corners of trees. A full check / scrub
> / etc would be needed to find out.
>