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
> ----- Original Message -----
> From: Steven Whitehouse <swhiteho redhat com
> <mailto:swhiteho redhat com
> To: Zama Ques <queszama yahoo in
<mailto:queszama yahoo in
> clustering <linux-cluster redhat com
<mailto:linux-cluster redhat com
> Sent: Thursday, 3 January 2013 3:46
> Subject: Re: [Linux-cluster] GFS without creating a cluster
> 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
> > 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.
> 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.