[Gluster-users] ... i was able to produce a split brain...

[Pranith Kumar Karampuri]

On 01/30/2015 06:28 PM, Jeff Darcy wrote:
>> Pranith and I had a discussion regarding this issue and here is what we have
>> in our mind right now.
>>
>> We plan to provide the user commands to execute from mount so that he can
>> access the files in split-brain. This way he can choose which copy is to be
>> used as source. The user will have to perform a set of getfattrs and
>> setfattrs (on virtual xattrs) to decide which child to choose as source and
>> inform AFR with his decision.
>>
>> A) To know the split-brain status :
>> getfattr -n trusted.afr.split-brain-status <path-to-file>
>>
>> This will provide user with the following details -
>> 1) Whether the file is in metadata split-brain
>> 2) Whether the file is in data split-brain
>>
>> It will also list the name of afr-children to choose from. Something like :
>> Option0: client-0
>> Option1: client-1
>>
>> We also tell the user what the user could do to view metadata/data info; like
>> stat to get metadata etc.
>>
>> B) Now the user has to choose one of the options (client-x/client-y..) to
>> inspect the files.
>> e.g., setfattr -n trusted.afr.split-brain-choice -v client-0 <path-to-file>
>> We save the read-child info in inode-ctx in order to provide the user access
>> to the file in split-brain from that child. Once the user inspects the file,
>> he proceeds to do the same from the other child of replica pair and makes an
>> informed decision.
>>
>> C) Once the above steps are done, AFR is to be informed with the final choice
>> for source. This is achieved by -
>> (say the fresh copy is in client-0)
>> e.g., setfattr -n trusted.afr.split-brain-heal-finalize -v client-0
>> <path-to-file>
>> This child will be chosen as source and split-brain resolution will be done.
> +1
>
> That looks quite nice, and AFAICT shouldn't be prohibitively hard to
> implement.
The only problem I see is kernel read caching which may come in the way. 
We may have to invoke fuse_invalidate if it comes in the way. We will 
find out once we implement this.

Pranith
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