[Linux-cluster] GFS without creating a cluster

[Zama Ques]

________________________________
 From: Digimer <lists at alteeve.ca>
To: Zama Ques <queszama at yahoo.in>; linux clustering <linux-cluster at redhat.com> 
Cc: Rajveer Singh <torajveersingh at gmail.com> 
Sent: Thursday, 3 January 2013 10:47 PM
Subject: Re: [Linux-cluster] GFS without creating a cluster
 
On 01/03/2013 10:22 AM, Zama Ques 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

Thanks Digimer for pointing the need of proper fencing setup . After configuring GFS , I did power down on one of the node and could see that the 
GFS mount point got hung on the other host as you have pointed out . Will now try to add fencing to the cluster. 

We are using HP Storage works for shared storage and accessing space from it using multipathing. 


Thanks
Zaman





Thanks Digimer. 
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