[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 <pkarampu at redhat.com 
> <mailto:pkarampu at redhat.com>> 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.
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