[Gluster-users] A few queries on self-healing and AFR (glusterfs 3.4.2)

[A Ghoshal]

Hello,

I have a replica-2 volume in which I store a large number of files that 
are updated frequently (critical log files, etc). My files are generally 
stable, but one thing that does worry me from time to time is that files 
show up on one of the bricks in the output of gluster v <volname> heal 
info. These entries disappear on their own after a while (I am guessing 
when cluster.heal-timeout expires and another heal by the self-heal daemon 
is triggered). For certain files, this could be a bit of a bother - in 
terms of fault tolerance...

I was wondering if there is a way I could force AFR to return 
write-completion to the application only _after_ the data is written to 
both replicas successfully (kind of, like, atomic writes) - even if it 
were at the cost of performance. This way I could ensure that my bricks 
shall always be in sync. 

The other thing I could possibly do is reduce my cluster.heal-timeout (it 
is 600 currently). Is it a bad idea to set it to something as small as 
say, 60 seconds for volumes where redundancy is a prime concern? 

One question, though - is heal through self-heal daemon accomplished using 
separate threads for each replicated volume, or is it a single thread for 
every volume? The reason I ask is I have a large number of replicated 
file-systems on each volume (17, to be precise) but I do have a reasonably 
powerful multicore processor array and large RAM and top indicates the 
load on the system resources is quite moderate.

Thanks,
Anirban
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