[Bugs] [Bug 1158008] New: Quota utilization not correctly reported for dispersed volumes

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1158008

            Bug ID: 1158008
           Summary: Quota utilization not correctly reported for dispersed
                    volumes
           Product: GlusterFS
           Version: mainline
         Component: disperse
          Assignee: bugs at gluster.org
          Reporter: xhernandez at datalab.es
                CC: bugs at gluster.org, gluster-bugs at redhat.com



Description of problem:

When quota is enabled on a dispersed volume, the real space usage is not
correctly tracked. Quota reports less used space than it's really been used by
the files stored on a directory.

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


How reproducible:

Always

Steps to Reproduce:
1. gluster volume create test disperse server{0..2}:/bricks/test
2. gluster volume start test
3. gluster volume quota test enable
4. gluster volume quota test limit-usage / 1GB
5. mount -t glusterfs server0:/test /gluster/test
6. dd if=/dev/zero of=/gluster/test/file bs=1024k count=512
7. gluster volume quota test list

Actual results:

It reports that there are 256MB used in '/'

Expected results:

It should say that there are 512 MB used if '/'

Additional info:

This is caused by an incorrect accounting of brick contents. Disperse volumes
store smaller files on each brick, and only one of these files is used to track
disk usage.

A workaround until this bug is solved is to assign a quota smaller than desired
to compensate for the incorrect computation. The exact value must be computed
this way:

N = Number of bricks of a disperse set
R = Redundancy
Q = Desired quota value
Q' = New quota value

Q' = Q / (N - R)

Then, instead of using:

    gluster volume quota <volname> limit-usage <path> Q

you should use:

    gluster volume quota <volname> limit-usage <path> Q'

When this bug is solved, all quota limits will need to be reverted back to the
original value (Q).

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