[Linux-cluster] Some questions - migrating from Sun to Red Hat cluster

[Thomas Sjolshagen]

 On Mon, 1 Nov 2010 22:45:11 -0600, Ivan Fetch <ifetch at du.edu> wrote:
> Hello,
>
> I have been using two CentOS 5.5 virtual machines, to learn Linux
> clustering, as a potential replacement for Sun (Sparc) clusters. We
> run Red Hat Enterprise Linux, but do not yet have any production
> cluster experience. I've got a few questions, which I'm stuck on:
>
> IS it possible to stop or restart one resource, instead of the entire
> resource group (service)? This can be handy when you want to work on 
> a
> resource (Apache), without having cluster restart it out from under
> you, but you still want your storage and IP to stay online. It seems
> like the clusvcadm command only operates on services; groups of
> resources.
>

 I don't know if this is the officially sanctioned way, but I tend to 
 freeze the group/service (clusvcadm -Z) and then use the start/stop 
 service script (service httpd reload, etc) to manipulate the daemons. 
 I've got a multi-daemon mail server service that brings up postfix + 
 amavisd + sqlgrey, ++ so this is handy here).

> What is the most common way to create and adjust service definitions
> - using Lusi, editing cluster.conf by hand, using command-line tools,
> or something else?
>

 I'm a die-hard CLI guy, so I tend to prefer editing by hand & 
 validating the cluster.conf file before loading it/using it (had a 
 couple of typo's that caused me grief as far as keeping things running 
 goes).
 
> For a non-global filesystem, which follows a service, is HA LVM the
> way to go? I have seen some recommendations against HA LVM, because
> LVM tagging being reset on a node, can allow that node to touch the
> LVM out-of-turn.
>
> What is the recommended way to make changes to an HA LVM, or add a
> new HA LVM, when lvm.conf on cluster nodes are already configured to
> tag? I have accomplished this by temporarily editing lvm.conf on one
> node, removing the tag line, and then making necessary changes to the
> LVM - it seems like there is likely a better way to do this.
>
> Will the use of a quarum disk, help to keep one node from fensing the
> other at boot (E.G> node1 is running, node2 boots and fenses node1)?
> This fensing does not happen every time I boot node2 - I may need to
> reproduce this and provide logs.

 I think, perhaps, you may need/want the <fence_daemon clean_start="1"> 
 included so as to avoid this? IIRC, setting clean_start helped me avoid 
 fencing of the surviving node at restart.

 I use the quorum disk to ensure less confusion by the nodes during 
 reboot scenarios too though.

 hth,

 // Thomas