Re: [Gluster-devel] regarding volume type change

[Pranith Kumar K]

On 02/23/2013 01:40 AM, Anand Avati wrote:

On Fri, Feb 22, 2013 at 5:39 AM, Pranith Kumar K <address@hidden> wrote:

hi,
      Could you let us know where is this feature used. I mean the use cases it addresses.

Can you be more specific about the question? Not sure I understand what you are trying to ask..

Avati 

Avati,
     Basically I want to understand the usecase the current implementation is trying to address. The problem I am concerned at the moment are the ones about data on different replicas. Especially the meaning of changelog it introduces on the files. It seems we can come up with use cases where the order of the replica subvolumes can change.

Ex: We can change replica old subvol-0 change log to be referred by subvol-1.

gluster --mode=script volume create r2 replica 2 pranithk-laptop:/home/gfs/r2_0 pranithk-laptop:/home/gfs/r2_1
volume create: r2: success: please start the volume to access data
gluster --mode=script volume start r2
volume start: r2: success
gluster --mode=script volume set r2 client-log-level DEBUG
volume set: success
gluster --mode=script volume set r2 brick-log-level DEBUG
volume set: success
mkdir: cannot create directory `/mnt/r2': File exists

gluster volume add-brick r2 replica 3 pranithk-laptop:/home/gfs/r2_2
volume add-brick: success

gluster volume remove-brick r2 replica 2 pranithk-laptop:/home/gfs/r2_0
Removing brick(s) can result in data loss. Do you want to Continue? (y/n) y
volume remove-brick commit force: success

gluster volume info
 
Volume Name: r2
Type: Replicate
Volume ID: 0e3eac61-5b99-455a-a0fc-818138d0ce1e
Status: Started
Number of Bricks: 1 x 2 = 2
Transport-type: tcp
Bricks:
Brick1: pranithk-laptop:/home/gfs/r2_1
Brick2: pranithk-laptop:/home/gfs/r2_2

This can potentially change the direction of self-heal. I was not able to find any documentation about this feature, except this http://community.gluster.org/q/volume-type-changes-supported-in-3-3-0/ The example I gave above is supported according to the link above, which is not good IMO. So I am trying to gather information about the status of this feature's implementation. What exact use cases are we trying to address?

Pranith.