Minimum size for lock disk

[Keith C. Patterson]

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

[John Poff]

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

[Jeff Schussele · Accepted solution]

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

[Michael Steele_2]

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.

[malay boy]

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

regards
mB

[John Poff]

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

[Duncan Edmonstone]

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

[Stuart Abramson_2]

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.

[Eugene Fleischmann]

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.