[Gluster-users] 2 nodes volume with existing data

[Anuradha Talur]

----- Original Message -----
> From: "CHEVALIER Pierre" <pchevalier at imajing.org>
> To: "Anuradha Talur" <atalur at redhat.com>
> Cc: gluster-users at gluster.org, "Pranith Kumar Karampuri" <pkarampu at redhat.com>, "Ravishankar N"
> <ravishankar at redhat.com>, "Atin Mukherjee" <amukherj at redhat.com>
> Sent: Thursday, May 19, 2016 6:17:50 PM
> Subject: Re: [Gluster-users] 2 nodes volume with existing data
> 
> 
> Le 19/05/2016 12:06, Anuradha Talur a écrit :
> >
> > ----- Original Message -----
> >> From: "Atin Mukherjee" <amukherj at redhat.com>
> >> To: "CHEVALIER Pierre" <pchevalier at imajing.org>, gluster-users at gluster.org
> >> Cc: "Pranith Kumar Karampuri" <pkarampu at redhat.com>, "Ravishankar N"
> >> <ravishankar at redhat.com>, "Anuradha Talur"
> >> <atalur at redhat.com>
> >> Sent: Tuesday, May 17, 2016 10:02:55 PM
> >> Subject: Re: [Gluster-users] 2 nodes volume with existing data
> >>
> >>
> >>
> >> On 05/17/2016 01:59 PM, CHEVALIER Pierre wrote:
> >>> Hi everyone,
> >>>
> >>> I have found a similar question in the ML but didn't find the answer I
> >>> wanted.
> >>> My situation is  the following :
> >>> We have 2 existing data storage unit with 72TB each, with 10TB left.
> >>> Currently these storage unit are synced using rsync periodically. We
> >>> want to tansform these 2 nodes into glusterfs bricks without loosing any
> >>> data or deleting a node.
> >>>
> >>> I was thinking setting up the 2 nodes with glusterfs in replica this way
> >>> :
> >>>
> >>> 1) Rsync server1/brick1 and server2/brick2 content
> >>> 2) Create the gluster replica and start :
> >>> gluster volume create volume1 replica 2 transport tcp server1:/brick1
> >>> server2:/brick1
> >>> gluster volume start volume1
> >> Gluster heavily depends on extended attributes for its business logic
> >> and hence configuring a brick with existing data means that the extended
> >> attributes would not be set for these files and hence this may not work
> >> as per the expectation.
> >>
> >> Given that you have a restriction using another brick, I'd suggest you
> >> to do the following:
> >>
> >> 1. Delete all the contents of server2/brick as this is a secondary copy
> >> 2. Create a plain distributed volume in server2 with server2/brick1
> >> 2. Start the volume
> >> 3. Mount the volume and then do copy the content from server1/brick1 to
> >> the mount point.
> >> 4. Probe server2 into the cluster
> >> 5. Perform an add-brick with server1/brick by gluster volume add-brick
> >> <volname> replica 2 <brick name> (Again make sure the content is deleted
> >> first)
> >> 6. This should trigger the self heal
> > As of now converting a plain distribute volume to distribute replicate is
> > not going to
> > automatically heal the files. (We are working on a solution for this.)
> >
> > If you really want to go ahead with this method then I'd recommend you to
> > do the following :
> >
> > 1) Stop I/O on your volume.
> > 2) Add the new brick.
> > 3) Stop and start your gluster volume
> > 4) Trigger lookup on the files from mount point by doing find . | xargs
> > stat on the mount point.
> >
> > This should trigger heals on the new brick.
> Hi,
> 
> OK this is good news,  I wanted to avoid to have no backup of the content.
> 
> So after that I mount the new volume as gluster fs and can start I/O on
> it  ?
> 
> Thanks for these informations.

Once you have completed the above mentioned steps, yes, you can mount the volume and start io on it.
> 
> >
> >> However since the data volume is very high, self heal can take a longer
> >> time to sync and finish.
> >>
> >> Also with a two node setup prevention of split brains is not guaranteed.
> >> An arbiter volume or a 3 way replica would be the solution to tackle
> >> this problem.
> >>
> >> Since I am not an AFR expert, I'd like to get a sign off from AFR team
> >> (In cc) before you try this out.
> >>
> >> ~Atin
> >> 	
> >>> Then, should I run a healing process, or stat each files in order to
> >>> self heal ?
> >>>
> >>> What happens if there is a slight difference between the 2 nodes,
> >>> mathematically if :
> >>> server1/brick1= server2/brick1+delta
> >>>
> >>> Will the delta part impact server1, or will it be lost  ?
> >>>
> >>> Maybe I worry for nothing, but as these 2 nodes host important data, I
> >>> wanted to make sure that eveything is OK.
> >>>
> >>> Thanks for your help !
> >>>
> >>> --
> >>> Pierre CHEVALIER
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> Gluster-users mailing list
> >>> Gluster-users at gluster.org
> >>> http://www.gluster.org/mailman/listinfo/gluster-users
> >>>
> --
> Pierre CHEVALIER
> 
> 

-- 
Thanks,
Anuradha.