topic Re: Minimum size for lock disk in Operating System - HP-UX

Minimum size for lock disk

Keith C. Patterson — Tue, 29 Apr 2003 19:35:59 GMT

Can anyone tell me what the minimum size for this is in ServiceGuard?
Thanks.

Re: Minimum size for lock disk

John Poff — Tue, 29 Apr 2003 19:58:55 GMT

Hi,

The lock disk can be any size. The information that MC/SG uses for the lock disk is written into the LVM header on the disk [I think it goes into the VGRA].

JP

Re: Minimum size for lock disk

Jeff Schussele — Tue, 29 Apr 2003 20:26:44 GMT

Hi Keith,

I think JP is correct i.e. the info is stored in the header....BUT....remember that the header occupies a single PE. So with the minimum PE size being 1 MB, The ABSOLUTE minimum would be a 1MB device.
Although I don't think it's supported, I've seen a cluster where an EMC gatekeeper volume was used & it was about 7MB if I remember correctly.

My 2 cents,
Jeff

Re: Minimum size for lock disk

Michael Steele_2 — Tue, 29 Apr 2003 20:44:59 GMT

Yep, that's right, its stored in the LVM header which is one PE and the default size for a PE is 4 mb.

The lock disk is nothing but something akin to a boolean variable, when owned, its flagged as owned and can't be taken away by another node within the cluster. Whichever node grabs it first during cluster start up gets ownership of the lock disk and ownership of the cluster, as well as the 'primary node' designation within the cluster.

Re: Minimum size for lock disk

malay boy — Tue, 29 Apr 2003 22:18:39 GMT

Guy's,
sorry for asking stupid question.whats PE ? and what is it used for .

regards
mB

Re: Minimum size for lock disk

John Poff — Wed, 30 Apr 2003 00:50:58 GMT

Hi MB,

That's not a dumb question at all.

PE stands for 'physical extent', which is the basic chunk of data you work with on a physical volume. In the logical volume manager [LVM], individual disks are initialized as physical volumes [PVs]. Each PV is subdivided into PEs. The standard size for a PE is 4 Mb. A PV also has an LVM header area where certain information about that PV is stored. One or more PVs are grouped together in a volume group [VG]. Then, you create logical volumes [LV] in a volume group which can be across one or more PVs.

That's a too short and too simple explanation of it all, but I hope it answers your question. HP offers a good three day class on LVM. You can take a look at the "Managing Systems and Workgroups" manual. It has a section on LVM under "Managing Files and Disks - Managing Disks":

http://docs.hp.com/hpux/onlinedocs/B2355-90742/B2355-90742.html

JP

Re: Minimum size for lock disk

Duncan Edmonstone — Wed, 30 Apr 2003 10:17:40 GMT

Keith,

remember that lock disks don't have to be dedicated to that task. Any disk in any of your shared volume groups can be a lock disk, and still contain data, so if you were thinking of just creating a small LUN on a disk array to serve as just the lock disk, there's no need.

HTH

Duncan

Re: Minimum size for lock disk

Stuart Abramson_2 — Wed, 30 Apr 2003 12:03:20 GMT

Duncan has the right idea.

DON'T waste a disk on the lock disk. Just make it the first PV in your first VG. They don't get that much traffic and won't affect performance.

DON'T use an EMC GateKeeper for you lock disk. They are NOT designed for that.

Re: Minimum size for lock disk

Eugene Fleischmann — Thu, 01 May 2003 16:28:14 GMT

While using the first vg in one of the pkgs in your cluster as the cluster lock volume may be tempting, be forewarned that if your application environment is dynamic (apps and therefore pkgs move to different servers and therefore different clusters, or an app/pkg is removed) your whole cluster may have to go down for a reconfiguration in order to accomodate that change. For dynamic application spaces, I recommend dedicating a PV as the cluster lock disk thereby isolating the cluster itself from dynamic changes in composition of its packages.