Hello Marek,
so if I understand correctly, you have 4 Veritas diskgroups, each diskgroup has 4-17 Luns of ~1TB each (so lets take max 17TB), You have created verias volumes & filesystems over it, & now these filesystems are approx full, now you would like to know which is better solution:
a) Create new diskgroup & add new luns here
b) Add new luns to existing diskgroups & resize volume & FS.
I hope my understanding is correct... if yes then see my answers below....
So lets consider both:
a) Create new diskgroup:- In this case, VXVM has no issues, would be a good choice to add new diskgroup as you will get new area for private region. There is a probability if there are too many objects (subdisks, volumes, plexes), private region config copy space would be utilized & there is no way in VXVM where you can resize length of private region without reinitializing. So creating new diskgroup would be a good idea however on the drawback side, it would increase administration work. If you are using a cluster (RAC/oracle as mentioned above), you will need to add new resource & put this new diskgroup into cluster configuration. Also linking of resources has to be done in correct fashion, you also will need to create new volumes & new filesystems & new mount points here (at VXVM layer) & put them in cluster control.
b) Adding space to existing diskgroup:- In this case unlike above, there would be less administration task, since diskgroup & volumes would be already under cluster control, you don't need to create any extra/new resources, however resize operation will be there.
If your filesystems are 100% full, it is likely that resize operation might fail, you need to bring down usage of FS before resizing it...
You also need to see if enough private region space is available & there are not too many objects....
You can find this by using following command:
# vxdg list <diskgroup> | grep "config:"
for example:
# vxdg list vrdg | grep "config:"
config: seqno=0.1139 permlen=48144 free=48131 templen=7 loglen=7296
as you can see above, I have good amount of free space in private region.
I hope this answers your query....
Gaurav