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From: Doug Ledford <dledford@redhat.com>
To: Jes Sorensen <jes.sorensen@redhat.com>, Guoqing Jiang <gqjiang@suse.com>
Cc: linux-raid@vger.kernel.org
Subject: Re: [PATCH 0/2] Check node nums for cluster raid
Date: Wed, 4 May 2016 11:19:17 -0400	[thread overview]
Message-ID: <305eaf9b-1275-f9b9-dae4-1be8f21ed98c@redhat.com> (raw)
In-Reply-To: <wrfjinytx3fv.fsf@redhat.com>

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On 05/04/2016 11:12 AM, Jes Sorensen wrote:
> Guoqing Jiang <gqjiang@suse.com> writes:
>> For cluster raid, we do need at least two nodes for it,
>> the two patches add the checks before create and change
>> bitmap.
>>
>> Thanks,
>> Guoqing    
>>
>> Guoqing Jiang (2):
>>   Create: check the node nums when create clustered raid
>>   super1: don't update node nums if it is not more than 1
>>
>>  Create.c | 7 ++++++-
>>  super1.c | 5 +++++
>>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> Hi Guoqing,
> 
> I am a little confused on this one - albeit I haven't looked at it in
> detail. Why should it not be possible to start a cluster with one node?
> In theory you should be able to do that, and then add nodes later?

Not typically.  A single node of a cluster is likely the odd man out, so
starting it and allowing changes to the underlying device has a high
potential of creating split brain issues.  For that reason, most cluster
setups require some minimum (usually 2) for a quorum before they will
start.  Otherwise, given a three node cluster, you could end up with
three separate live filesystems and the need to merge changes between
them to bring the cluster back into sync.


-- 
Doug Ledford <dledford@redhat.com>
              GPG KeyID: 0E572FDD



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  reply	other threads:[~2016-05-04 15:19 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-04  8:33 [PATCH 0/2] Check node nums for cluster raid Guoqing Jiang
2016-05-04  8:33 ` [PATCH 1/2] Create: check the node nums when create clustered raid Guoqing Jiang
2016-05-04  8:33 ` [PATCH 2/2] super1: don't update node nums if it is not more than 1 Guoqing Jiang
2016-05-04 15:12 ` [PATCH 0/2] Check node nums for cluster raid Jes Sorensen
2016-05-04 15:19   ` Doug Ledford [this message]
2016-05-04 15:25     ` Jes Sorensen
2016-05-04 15:28       ` Doug Ledford
2016-05-05  3:03   ` Guoqing Jiang
2016-05-05 20:28     ` Jes Sorensen

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