Thinking about it more, I'd still rather have this functionality exposed
at the client through xattrs. For 5 years I've thought about this, and
the more I encounter split-brain, the more I think this is the needed
approach.
"getfattr -n trusted.glusterfs.stat" returns
xml/json/some_madeup_datastructure with the results of stat from each brick
"getfattr -n trusted.glusterfs.afr" returns the afr matrix
"setfattr -n trusted.glusterfs.sb-pick -v "server2:/srv/brick1"
That gives us the tools we need to choose what to do with any given
split-brain. For large swaths of automated repair, we can use find.
I suppose that last bit could still be implemented through that cli command.
On 08/07/2014 01:35 AM, Ravishankar N wrote:
Manual resolution of split-brains [1] has been a tedious task
involving understanding and modifying AFR's changelog extended
attributes. To simplify and to an extent automate this task, we are
proposing a new CLI command with which the user can specify what the
source brick/file is, and automatically heal the files in the
appropriate direction.
Command: gluster volume resolve-split-brain <VOLNAME> {<bigger_file>
| source-brick <brick_name> [<file>] }
Breaking up the command into its possible options, we have:
a) gluster volume resolve-split-brain <VOLNAME> <bigger_file>
When this command is executed, AFR will consider the brick having the
highest file size as the source and heal it to all other bricks
(including all other sources and sinks) in that replica subvolume. If
the file size is same in all the bricks, it does *not* heal the file.
b) gluster volume resolve-split-brain <VOLNAME > source-brick
<brick_name > [<file>]
When this command is executed, if <file> is specified, AFR heals the
file from the source-brick <brick_name> to all other bricks of that
replica subvolume. For resolving multiple files, the command must be
run iteratively, once per file.
If <file> is not specified, AFR heals all the files that have an entry
in .glusterfs/indices/xattrop *and* are in split-brain. As before,
heals happen from source-brick <brick_name> to all other bricks.
Future work could also include extending the command to add other
policies like choosing the file having the latest mtime as the source,
integration with trash xlator wherein the files deleted from the sink
are moved to the trash dir etc.
Please give feedback on the above.
Regards,
Ravi
[1] https://github.com/gluster/glusterfs/blob/master/doc/split-brain.md
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