DO I NEED A VG PER APLICATION IN MC/SG?

[Sebastian Viudez Ortega]

We have recently purchased a cluster
composed by two rp5470 and one VA7100 with
4 disk of 36G. There's also two fiber controlers
per node and two hubs, to provide path
redundancy to the SAN.

Our intention is, based at the ServiceGuard,
tu put in high availability 3 or 4 little
independent aplications per node (active-active
configuration).

Our main doubt is about the raid and Volume
Group configuration. If we have only one VG and
several Logical Volumes -one per aplication-,
it seems that we must activate the VG from
both nodes simultaneously. It this possible?

If not, do we need a VG per aplication to
get the ServiceGuard package's independence?

Thank you in advance

[melvyn burnard]

A VG can belong to one, and ONLY one, ServiceGuard Package.
A ServiceGuard package does not need to have a VG, if the application does not need a VG, and a package can have multiple VG's.

Therefore, if you want to have four packages, and each package is to have a VG, then you need a minimum of 4 VG's

Take a read through Managing MC/ServiceGuard manual available at:
http://docs.hp.com/hpux/ha

[Darrell Allen]

Hi,

ServiceGuard requires VGs be activated by only one node at a time. The package requires exclusive access to it's VG(s).

Another note, you can have more than one application in a package. With 4 apps you could have from 1 to 4 packages just depending on how you want to split it up. Of course, if all 4 apps are in one package then all 4 apps run on one server and the other server would be idle until the package failed over. But if you have only 2 nodes and can evenly distribute the load of the applications you could package some of the apps together, say 2 and 2. That could help if you are short on "disks" and VGs.

Darrell

[Roger Baptiste · Accepted solution]

<Group configuration. If we have only one VG and several Logical Volumes -one per aplication->>

You would definitely need atleast ONE VG PER NODE. That's because for a regular CLuster
the nodes use VG "exclusively" (only one node can accesss the VG at any time).

You would need to decide the number of VG's for each node. Since you have four applications per node (or is it two?), you have the choice of having one VG per application or using One vg for all the applications in the node. The later option may limit your flexibility for maintaining the VG, but you can live with it.

<both nodes simultaneously. It this possible? >>

Nope. Only one VG per node, unless it is a OPS Cluster. (OPS cluster is for Oracle applications which share VG's and have only raw volumes ).

<get the ServiceGuard package's independence>>

Definitely. It gives you the best flexibility in maintaining the cluster. For eg:
Node 1:
PkgA -> consists of VG01 (running app1)
PKGB -> consists of VG02 (running app2)
Node 2:
PKGC -> ....
PKGD -> ..

and so on. That way, you can switch any application from one node to another without affecting the others.

HTH
raj

[Sanjay_6]

Hi Sebstian,

Each Service Guard package should have its own VG that is not assiciated with other packge VG's and the system VG's. Depending on which system the packge is running, the VG gets activated on that VG. That VG moves from one node to another with the packge being moved from one node to another.

Also have a look at the SG faq for more info,

http://docs.hp.com/hpux/onlinedocs/ha/haFAQindex2.html

Hope this helps.

Regds

[Sebastian Viudez Ortega]

Melvyn, Darrell, raj, sanjay, very thank you.

I had a look at the Managing MC/ServiceGuard
manual -september 2001 Edition- and I was
suspecting something as this.

The problem is that to put 8 applications -4 per
node- in HA with MCSG we need 8 VG's (we would like
to design packages in a independent way, say a
package per application). It seems too much VG's!
By the way, how many VG's you can config in a
VA7100? (Installed as RAID, not as JBOD).

Well, in any case it seems that ServiceGuard
does not adjust very well at our situation. We have
several diferents database engine -Oracle, Basis Plus,
BRS, Eloquence- and applications that does not waste
very much disk space -a few Gigas each one-. Although
availability is not excessively critical, the idea was
take advantage of HA to do the admin tasks, without
interruption of the service,
during the working day.

S. Viudez.

[melvyn burnard]

As the VA7100 is an array, you can set it up to give you as many Physical devices as you wish to see, within limits.
you can then use these PV's to create VG's, and as each VG need only consist of one PV, then that is your limitation as to how many VG's you create.

[Santosh Nair_1]

Another thing to remember is that by default the OS only supports 10 VGs, vg00 through vg09 (using the standard naming convention). This is controlled by the kernel parameter maxvgs. If you need more than 10 VGs then you need to increase this kernel parameter (which requires a reboot, etc.).

-Santosh

[Sanjay_6]

Hi Sebastian,

Other than keeping the kernel parameter "maxvgs" in mind also remeber that the VG's don't share disks. A Disk is part of only one VG. Like Melvyn said, you can create disk slices as per your requirements.

It would be a good idea to group application and limit the no. of applications. This way you can limit the number of VG's you may need and will also be in a better position to use disks of higher capacities.

Hope this helps.

Regds

[Sebastian Viudez Ortega]

Hi melvyn,

How can i set the VA7100 up
to give me as many Physical
devices as i wish?

I've read the VA7100 Installation Guide and
the User's & Service Guide
and i cannot find about this,
do you know any document
more complete in the matter?

S. Viudez.