[Gluster-users] Heal operation detail of EC volumes

[Ashish Pandey]

----- Original Message -----

From: "Serkan Çoban" <cobanserkan at gmail.com> 
To: "Gluster Users" <gluster-users at gluster.org> 
Sent: Monday, May 29, 2017 5:13:06 PM 
Subject: [Gluster-users] Heal operation detail of EC volumes 

Hi, 

When a brick fails in EC, What is the healing read/write data path? 
Which processes do the operations? 

Healing could be triggered by client side (access of file) or server side (shd). 
However, in both the cases actual heal starts from "ec_heal_do" function. 


Assume a 2GB file is being healed in 16+4 EC configuration. I was 
thinking that SHD deamon on failed brick host will read 2GB from 
network and reconstruct its 100MB chunk and write it on to brick. Is 
this right? 

You are correct about read/write. 
The only point is that, SHD deamon on one of the good brick will pick the index entry and heal it. 
SHD deamon scans the .glusterfs/index directory and heals the entries. If the brick went down while IO was going on, index will be present on killed brick also. 
However, if a brick was down and then you started writing on a file then in this case index entry would not be present on killed brick. 
So even after brick will be UP, sdh on that brick will not be able to find it out this index. However, other bricks would have entries and shd on that brick will heal it. 

Note: I am considering each brick on different node. 

Ashish 










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