Created attachment 593160 [details]
patch to fix the problem

Description of problem:

if you set read-subvolume in volume file or over xlator-options it has no effect
of which subvolume the client chooses.

when read-subvolume is set the client should try to read first from that subvolume if its online.

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

3.3.0

How reproducible:

glusterfs --volfile-id=testvol --volfile-server=gluster02 --xlator-option=testvol-replicate-0.read-subvolume=testvol-client-1 /mnt2

then read files from the volume
  
Actual results:

the option gets acceptet:
[options.c:1043:xlator_option_init_xlator] 0-testvol-replicate-0: option read-subvolume using set value testvol-client-1
[afr-common.c:1294:afr_lookup_select_read_child] 0-testvol-replicate-0: Source selected as 0 for /a.1


Expected results:

the option gets acceptet:
[options.c:1043:xlator_option_init_xlator] 0-testvol-replicate-0: option read-subvolume using set value testvol-client-1
[afr-common.c:1294:afr_lookup_select_read_child] 0-testvol-replicate-0: Source selected as 1 for /a.1


Additional info:

the problem seems to be in afr-common.c 
in function afr_select_read_child_from_policy

if the config option read-subvolume is set it should be preferred for read

see my patch