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Re: [Linux-cluster] GFS without creating a cluster






From: Digimer <lists alteeve ca>
To: Zama Ques <queszama yahoo in>; linux clustering <linux-cluster redhat com>
Cc: Rajveer Singh <torajveersingh 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 redhat com
>    <mailto:swhiteho redhat com>>
>    To: Zama Ques <queszama yahoo in <mailto:queszama yahoo in>>; linux
>    clustering <linux-cluster redhat com <mailto:linux-cluster 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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