[Linux-cluster] Design question about VG / LV in a clustered environement

[Nicolas Ross]

Hi !

Since the last couple of months, we had a few problems with the maner we 
designed our clustered filesystem and we are planing to do a re-design of 
the filesystems and how they are used.

Our cluster is composed of 8 nodes, connected via fibre channel, to a raid 
enclosure where we have 6 pair of 1-tb drives in mirror, so 6 1tb physical 
volumes.

First of all, our services that are run from the cluster are running inside 
of directories. For exemple, a webserver for a given application is run from 
/CyberCat/WebServer/(...) That directory contains all executable (apache, 
php for exemple) and the related data, except for the databases. /CyberCat 
being a single GFS partition containing several other services.

This filesystem and another one like this containing services for some other 
clients occupy a single VG composed of 2 PV (total 2tb). The remaining (4) 
other PV are used in one 1tb VG each, and those VG contains only one LV that 
is used for databases servers.

For availibility reasons, we are planing of spliting the /CyberCat (and the 
other one like it) FS into several smaller filesystems, one for each 
service.

The reason being that in the event that we need to make a filesystem check, 
or any other unplaned reason, on any filesystem it won't affect other 
services.

So, now comes the question I have :

1. First of all, is this a bad idea ?

2. Is there any disadvantages of doing a single volume group composed of 
many physical volumes, enabling us to move the extents of a logical volume 
from one physical volume to another one, so that load is more balanced in 
the event we need it.

Thanks for the input.