Description of problem:
-----------------------

(Thanks Ravi for the catch!) 

Create rep2/3 volume on 3.3 bits..

I see that client-io-threads is getting loaded for newly created volumes :

[root@gqas013 rep]# cat rep.tcp-fuse.vol 
volume rep-client-0
    type protocol/client
    option send-gids true
    option event-threads 4
    option transport.address-family inet
    option transport-type tcp
    option remote-subvolume /bricks10/A1
    option remote-host gqas013
    option ping-timeout 42
end-volume

volume rep-client-1
    type protocol/client
    option send-gids true
    option event-threads 4
    option transport.address-family inet
    option transport-type tcp
    option remote-subvolume /bricks10/A1
    option remote-host gqas005
    option ping-timeout 42
end-volume

volume rep-client-2
    type protocol/client
    option send-gids true
    option event-threads 4
    option transport.address-family inet
    option transport-type tcp
    option remote-subvolume /bricks10/A1
    option remote-host gqas006
    option ping-timeout 42
end-volume

volume rep-client-3
    type protocol/client
    option send-gids true
    option event-threads 4
    option transport.address-family inet
    option transport-type tcp
    option remote-subvolume /bricks11/A1
    option remote-host gqas013
    option ping-timeout 42
end-volume

volume rep-client-4
    type protocol/client
    option send-gids true
    option event-threads 4
    option transport.address-family inet
    option transport-type tcp
    option remote-subvolume /bricks11/A1
    option remote-host gqas005
    option ping-timeout 42
end-volume

volume rep-client-5
    type protocol/client
    option send-gids true
    option event-threads 4
    option transport.address-family inet
    option transport-type tcp
    option remote-subvolume /bricks11/A1
    option remote-host gqas008
    option ping-timeout 42
end-volume

volume rep-replicate-0
    type cluster/replicate
    option use-compound-fops off
    subvolumes rep-client-0 rep-client-1 rep-client-2
end-volume

volume rep-replicate-1
    type cluster/replicate
    option use-compound-fops off
    subvolumes rep-client-3 rep-client-4 rep-client-5
end-volume

volume rep-dht
    type cluster/distribute
    option lock-migration off
    option lookup-optimize on
    subvolumes rep-replicate-0 rep-replicate-1
end-volume

volume rep-write-behind
    type performance/write-behind
    subvolumes rep-dht
end-volume

volume rep-read-ahead
    type performance/read-ahead
    subvolumes rep-write-behind
end-volume

volume rep-readdir-ahead
    type performance/readdir-ahead
    option rda-cache-limit 10MB
    option rda-request-size 131072
    option parallel-readdir off
    subvolumes rep-read-ahead
end-volume

volume rep-io-cache
    type performance/io-cache
    subvolumes rep-readdir-ahead
end-volume

volume rep-quick-read
    type performance/quick-read
    subvolumes rep-io-cache
end-volume

volume rep-open-behind
    type performance/open-behind
    subvolumes rep-quick-read
end-volume

volume rep-md-cache
    type performance/md-cache
    subvolumes rep-open-behind
end-volume

volume rep-io-threads
    type performance/io-threads    // THIS HERE
    subvolumes rep-md-cache
end-volume

volume rep
    type debug/io-stats
    option count-fop-hits off
    option latency-measurement off
    option log-level INFO
    subvolumes rep-io-threads
end-volume
[root@gqas013 rep]# 


Version-Release number of selected component (if applicable):
-------------------------------------------------------------

3.8.4-25

How reproducible:
-----------------

Always.


Additional info:
-----------------

[root@gqas013 rep]# gluster v info rep
 
Volume Name: rep
Type: Distributed-Replicate
Volume ID: ef19f98e-18cd-417a-bada-769afafd3125
Status: Started
Snapshot Count: 0
Number of Bricks: 2 x 3 = 6
Transport-type: tcp
Bricks:
Brick1: gqas013:/bricks10/A1
Brick2: gqas005:/bricks10/A1
Brick3: gqas006:/bricks10/A1
Brick4: gqas013:/bricks11/A1
Brick5: gqas005:/bricks11/A1
Brick6: gqas008:/bricks11/A1
Options Reconfigured:
ganesha.enable: on
features.cache-invalidation: off
client.event-threads: 4
server.event-threads: 4
cluster.lookup-optimize: on
transport.address-family: inet
nfs.disable: on
nfs-ganesha: enable
cluster.enable-shared-storage: enable
[root@gqas013 rep]#