Feature page for Rebalance Estimates

Change-Id: I086a9bfb15a47668fe28684e480d6230fd3e7811
Signed-off-by: N Balachandran <[email protected]>
Reviewed-on: http://review.gluster.org/16119
Reviewed-by: Shyamsundar Ranganathan <[email protected]>
Tested-by: Shyamsundar Ranganathan <[email protected]>

Author: N Balachandran

under_review/rebalance-estimates.md

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+Feature
+-------
+
+Summary
+-------
+
+Provide a user interface to determine when the rebalance process will complete
+
+Owners
+------
+Nithya Balachandran <[email protected]>
+
+
+Current status
+--------------
+Patch being worked on.
+
+
+Related Feature Requests and Bugs
+---------------------------------
+https://bugzilla.redhat.com/show_bug.cgi?id=1396004
+Desc: RFE: An administrator friendly way to determine rebalance completion time
+
+
+Detailed Description
+--------------------
+The rebalance operation starts a rebalance process on each node of the volume.
+Each process scans the files and directories on the local subvols, fixes the layout
+for each directory and migrates files to their new hashed subvolumes based on the
+new layouts.
+
+Currently we do not have any way to determine how long the rebalance process will
+take to complete.
+
+The proposed approach is as follows:
+
+ 1. Determine the total number of files and directories on the local subvol
+ 2. Calculate the rate at which files have been processed since the rebalance started
+ 3. Calculate the time required to process all the files based on the rate calculated
+ 4. Send these values in the rebalance status response
+ 5. Calculate the maximum time required among all the rebalance processes
+ 6. Display the time required along with the rebalance status output
+
+
+The time taken is a factor or the number and size of the files and the number of directories.
+Determining the number of files and directories is difficult as Glusterfs currently
+does not keep track of the number of files on each brick.
+
+The current approach uses the statfs call to determine the number of used inodes
+and uses that number as a rough estimate of how many files/directories ae present
+on the brick. However, this number is not very accurate because the .glusterfs
+directory contributes heavily to this number.
+
+Benefit to GlusterFS
+--------------------
+Improves the usability of rebalance operations.
+Administrators can now determine how long a rebalance operation will take to complete
+allowing better planning.
+
+
+Scope
+-----
+
+#### Nature of proposed change
+
+Modifications required to the rebalance and the cli code.
+
+#### Implications on manageability
+
+gluster volume rebalance <volname> status output will be modified
+
+#### Implications on presentation layer
+
+None
+
+#### Implications on persistence layer
+
+None
+
+#### Implications on 'GlusterFS' backend
+
+None
+
+#### Modification to GlusterFS metadata
+
+None
+
+#### Implications on 'glusterd'
+
+None
+
+How To Test
+-----------
+
+Run a rebalance and compare the estimates with the time actually taken to complete
+the rebalance.
+
+The feature needs to be tested against large workloads to determine the accuracy
+of the calculated times.
+
+User Experience
+---------------
+
+Gluster volume rebalance <volname> status
+will display the expected time left for the rebalance process to complete
+
+
+Dependencies
+------------
+
+None
+
+Documentation
+-------------
+
+Documents to be updated with the changes in the rebalance status output.
+
+
+Status
+------
+In development.
+
+
+
+Comments and Discussion
+-----------------------
+
+*Follow here*