[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 <
landman at scalableinformatics.com> 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"<anand.avati at gmail.com> To: landman at scalableinformatics.com Cc:
>> "Gluster Devel"<gluster-devel at nongnu.org> 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<
>> landman at scalableinformatics.com>  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: landman at scalableinformatics.com
> web  : http://scalableinformatics.com
>       http://scalableinformatics.com/sicluster
> phone: +1 734 786 8423 x121
> fax  : +1 866 888 3112
> cell : +1 734 612 4615
>
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