[Gluster-users] heal questions

[Ravishankar N]

On 11/19/2014 03:23 AM, Lindsay Mathieson wrote:
> Just some basic question on the heal process, please just point me to the docs 
> if they are there :)
> 
> - How is the need for a heal detected? I presume nodes can detect when they 
> can't sync writes to the other nodes. This is flagged (xattr?) for healing 
> when the other nodes are back up?
> 
> - How is the master file chosen? quorum? latest write?

Self heal is detection/healing is handled by AFR using extended attributes which keep track of the type of heal (data/meta-data/entry) and the direction of heal (i.e. what the sources and sinks are).
More details can be found here :https://github.com/gluster/glusterfs/blob/master/doc/features/afr-v1.md


> 
> - I have a three peer, two node/brick replica with server side quorum. The 
> third peer was added to give an odd number of peers for quorom, but it doesn't 
> participate in bricks. Does this make sense? it helps with deciding which node 
> is master for heals?

Server quorum is useful for detecting split-brains due to graph change, etc but I guess it can still lead to data split-brains. Client quorum can be used to avoid data split-brains at the cost of
availability. More information here:

https://access.redhat.com/documentation/en-US/Red_Hat_Storage/2.1/html/Administration_Guide/ch10s10.html
https://access.redhat.com/documentation/en-US/Red_Hat_Storage/2.0/html/Administration_Guide/sect-User_Guide-Managing_Volumes-Quorum.html
http://www.gluster.org/community/documentation/index.php/Features/Server-quorum



> 
> - diff heals. I'm guessing the nodes scan the file pairs block by block, 
> calculating a checksum for each block and comparing, if they don't match, the 
> master node block is replicated.

That is correct. It scans in 128 kb chunks (configurable via the `cluster.self-heal-window-size` volume set option).
> 
> - Synchronizing the compare over the network must be fun ...
>   
> 
> - Is there anyway to display a file heal progress? it would make the process a 
> lot less anxiety inducing even if it was very slow.

As of now, `gluster volume heal <volname> info` gives only the list of files that need healing. But yes, it would be nice to have some sort of a CLI to monitor the % progress of files that are
currently under data self-heal.


HTH,
Ravi

> 
> thanks,
> 
> 
> 
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