Re: [Gluster-devel] [PATCH] Enable replica 1 mirror creation for mirrored volumes

[Anand Avati]

We have plans of introduction the option to scale up/down replication counts on a volume. This way you can move between distributed and distributed-replicated volumes by doing add-brick with a proper 'replica N' parameter. Running replicate with a single subvolume is something we don't test and do not recommend/support.

Avati

On Mon, May 30, 2011 at 5:18 AM, Joe Landman <address@hidden> wrote:

On 05/29/2011 07:31 PM, Craig Carl, Gluster wrote:

Avati - This type of functionality is incredibly useful from an IT
operations POV, my thinking is it would make migrating from a
distribute only to a distribute-replica volume easier.

Actually, this is what I had in mind.  This was only the very first step.  I was starting to look at the logic underneath the replicate setup.  My initial guess is that all it would really take to enable this is a sequence of

       create with missing mirror
       add-brick to mirror

Then growth (add-brick) to grow.  Rebalance after add.

I don't think there needs to be much additional code for this.  Will be trying it soon on one of our internal units.  The change in this case is a single line really, and it just lowers the limit for the mirror to 1.

An alternative, and similar to linux MD RAID, is to use the "missing" keyword. This could be useful in setting up a larger mirror with initial portion missing.  This might make sense for geo-replication as well (create 1/2 of the replica, and add the next portion as a mirror, leveraging rsync and inotify events).

Craig


----- Original Message ----- From: "Anand
Avati"<address@hidden> To: address@hidden Cc:
"Gluster Devel"<address@hidden> Sent: Saturday, May 28,
2011 8:12:18 AM Subject: Re: [Gluster-devel] [PATCH] Enable replica 1
mirror creation for mirrored volumes


Joe, Can you shed some more light on the use case? What purpose is
the replicate translator serving without the second server? In what
way is this more beneficial than loading the replicate translator
only when the second server is introduced to the system?


Avati


On Sat, May 28, 2011 at 7:11 PM, Joe Landman<
address@hidden>  wrote:


This patch to the cli enables a very simple replica 1 mirror creation
(similar to the "missing" attribute for mdadm RAID1 creation).

It will likely need additional supporting work in add-brick so that
incomplete mirrors are assembled correctly for distributed-replicated
cases.

Building/Assembling an incomplete mirror is an important capability
needed for a number of use cases.

--
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics, Inc.
email: address@hidden
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