# Re: \[PATCH 0/2\] Check node nums for cluster raid

- From: Doug Ledford \<hidden\>
- Date: 2016-05-04 15:19:17 
- List: linux-raid
- Page: https://ratatoskr.run/linux-raid/2016/05/6632012
- Thread: https://ratatoskr.run/linux-raid/2016/05/6632011/t.md

```text
On 05/04/2016 11:12 AM, Jes Sorensen wrote:
> Guoqing Jiang [ref] 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 [ref]
              GPG KeyID: 0E572FDD


```

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