[Linux-cluster] GFS without creating a cluster

[Digimer]

On 01/03/2013 10:22 AM, Zama Ques wrote:
> 
> 
> ------------------------------------------------------------------------
> *From:* Rajveer Singh <torajveersingh at gmail.com>
> *To:* Zama Ques <queszama at yahoo.in>; linux clustering
> <linux-cluster at redhat.com>
> *Cc:* Steven Whitehouse <swhiteho at redhat.com>
> *Sent:* Thursday, 3 January 2013 8:38 PM
> *Subject:* Re: [Linux-cluster] GFS without creating a cluster
> 
> 
> 
> On Thu, Jan 3, 2013 at 7:07 PM, Zama Ques <queszama at yahoo.in
> <mailto:queszama at yahoo.in>> wrote:
> 
> 
> 
> 
> 
> 
>     ----- Original Message -----
>     From: Steven Whitehouse <swhiteho at redhat.com
>     <mailto:swhiteho at redhat.com>>
>     To: Zama Ques <queszama at yahoo.in <mailto:queszama at yahoo.in>>; linux
>     clustering <linux-cluster at redhat.com <mailto:linux-cluster at redhat.com>>
>     Cc:
>     Sent: Thursday, 3 January 2013 3:46 PM
>     Subject: Re: [Linux-cluster] GFS without creating a cluster
> 
>     Hi,
> 
>     On Thu, 2013-01-03 at 18:00 +0800, Zama Ques wrote:
>     > Hi All ,
>     >
>     >
>     > Need few clarification regarding GFS.
>     >
>     >
>     > I need to create a shared file system for our servers . The
>     servers will write to the shared file system at the same time and
>     there is no requirement for a cluster .
>     >
>     > Planning to use GFS but GFS requires cluster software to be
>     running . My confusion here is If I just run the cluster software (
>     cman etc ) without creating a cluster , will I be able to configure
>     and run GFS2. Also , is it possible to write to a GFS file system
>     from many servers at the same time ?
>     >
>     > Will be great if somebody can clarify by doubts.
>     >
>     >
>     > Thanks in Advance
>     > Zaman
>     >
>     >
> 
>     > If you want to use GFS2 without a cluster, then you'll only be able to
>     > use it from a single node (just like if you were using ext3 for
>     > example). If you want to use GFS2 as intended, with multiple nodes
>     > accessing the same filesystem, then you'll need to set up a cluster in
>     > order to do so,
> 
>     Thanks Steve for the reply . As you said setting up a cluster is
>     needed to use GFS2 with multiple nodes, does that mean that I need
>     to create cluster.conf or running cluster services (cman etc) should
>     be fine for setting up GFS2. Not sure whether cman will run without
>     creating cluster.conf
> 
>     Assuming that I need to setup cluster.conf in order to use GFS2 ,
>     that means if there are two nodes in the cluster with GFS2 as file
>     system resource , GFS2 will be mounted on only one host based on
>     failover domain policy . But our requirement is like that GFS2
>     should be mounted on both servers at the same time  . Based on my
>     little understanding of GFS , looks to me that I will not be able to
>     achieve this using GFS2 or there are some way to achieve this ?
> 
>     Please clarify on this.
> 
>  > Hi Zama,
>> As steve said, you must have to configure proper cluster to use GFS2
> filesystem and mounted on multiple nodes at the same time so that all
> can > access it. You do not need to configure GFS2 filesystem to be
> managed by cluster i.e. rgmanager. but just make the entry in /etc/fstab
> file as like > normal ext3 filesystem.
>> I hope, it answers your question.
> 
> Thanks Rajveer for clarifying . I think I am clear now . Will now try to
> configure GFS2.
> 
> 
> Thanks
> Zaman

Note that you will also need proper fencing setup (usually using the
nodes' IPMI interface). Without properly configured, tested fencing, the
first time a node fails the GFS2 partition will hang (by design).

The reason the cluster is needed is that the access to the shared
storage and file system has to be coordinated between the nodes so that
one node doesn't step on the other. This is possible thanks to DLM;
distributed lock manager. DLM uses the cluster communications, hence the
need for the cluster.

Note also that you need shared storage, obviously. iSCSI or DRBD if you
only have two nodes.

Please take a look at this link. It explains in details how this works;

https://alteeve.ca/w/2-Node_Red_Hat_KVM_Cluster_Tutorial#Concept.3B_Fencing

-- 
Digimer
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