Bikramjeet Vig created IMPALA-5574:
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             Summary: Add Backend tests for DiskIOMgr and add ability to 
specify disks to be used by impala
                 Key: IMPALA-5574
                 URL: https://issues.apache.org/jira/browse/IMPALA-5574
             Project: IMPALA
          Issue Type: Improvement
          Components: Backend
            Reporter: Bikramjeet Vig
            Priority: Minor


As a part of the effort for IMPALA-5240, a bug was identified where impala 
would crash if num_disks are set more than the number of logical disks on 
system and num_threads_per_disk is not set. This bug also lets the user create 
more disk queues than the num of logical disks which would eventually never be 
used.

Existing test cases in disk-io-mgr-test were identified that exploited this bug 
by setting num_disks more than available logical disks and sometimes even using 
those extra disk queues being created as a result of this. This will be fixed 
in IMPALA-5240 by explicitly setting num_disks in each test to 1. Moreover, 
since only one file was created and used in each test, effectively only one 
disk was being used. Therefore as a part of this jira the following tasks have 
been identified:

1. add test cases to exercise code paths that use more than one disk (only if 
multiple disks are available on the system)
2. more clearly define the semantics of using num_disks as a config parameter, 
that is, if a user specifies less num of disks than available then they should 
also have the ability to specify the disks that they want, a possible solution 
can be to have comma separated paths that link folders on separate disks



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