Extend new disk device into VG vgeva5 in production setting

[Frank Copeland]

Our hpux 11.11 system (pa-risc) includes a VG called vgeva5. We run on an rp4720. The DBserver is a vPar with 6 CPU's and 10GB of memory allocated to it. It's usually pretty strong. It is composed of 16-20GB luns / vdisks from our EVA-5K. An on-line Informix DB resides in this VG and needs a little more expansion room for DB spaces. I'm the DBA and system admin. I want to create a new 10GB v-disk on the EVA and extend this into vgeva5 while the Informix database is up and running.
At a high level I will:
1. use command view GUI to create a 10GB v-disk
2. present new v-disk to DBserver
3. ioscan -fnC disk on the DBserver
4. insf for the new disk
(do I have to pvcreate here?)
5. vgextend the new disk into vgeva5
6. lvcreate new 2GB lvols into the newly extended space.

My big concern is that I can perform the vgextend (pvcreate?) and lvcreates with minimal performance hit while vgeva5 (and informix) is up and running.
My experience with the EVA has been rewarding. We have seen nothing but performance improvments over the old VA technology since installing it a year ago. This is my first time submitting a question on the forum though I've used it for resarch many times. Thanks to everyone who contributes.

[Simon Hargrave]

Yes you do need to do the pvcreate

There's absolutely no problem doing this online, it's pretty standard practice.

However I would question your 2Gb lvol sizing. Is this just an in-house historical thing? Is it an Informix recommendation?

There's no real advantage to this since it gives you no physical separation on disks from a performance striping perspective, this is all done at the EVA level.

[Frank Copeland]

Thanks for quick resonse.
The 2GB lvol size is DB specific requirement. Informix allows 2GB max size chunks to be added to the database (done dynamically) or 4GB max size in newer versions of informix. We may add any size less than 2GB (or 4GB) as a new chunk but not more.

[Simon Hargrave]

Sorry yes I remember, Informix is raw LV's not filesystems. That makes sense.

[Ninad_1]

Frank,

True - even though you would be adding 2GB volumes to your informix database - does not restrict you from having a PV in your VG of size >2GB, because you can create 2GB lvols in the VG that will be using this new PV.
And yes you always need to initialise a new disk/LUN using pvcreate in order to LVM to use it.

Regards,
Ninad

[Frank Copeland]

Well I have finished my effort. Not really a solution but another path to take.

I'll explain. After completing all the steps successfully we then ran the extendvg on the new 10GB vdisk. Took the error "to many links". OUCH! The 300GB VG was created with the default of Max PV 16 which is how many luns I already have in the VG. From what I understand the only correction for that situation is a full rebuild of the entire VG (that would include production DB restore for me), next time setting the Max PV to a greater value ( I think up to 256, like Max LV which I know is 256). So I have 230 LVs created within the VG now and have growth for no more than 26 more lvols and then only with the remaining space left free in my VG. Well, I have enough free extents in the existing VG to make a few, maybe several, more 2GB lvols and for the present few months of summer. Beyond that I gotta get that Archive DB up and going so I can get my data purge project cranked up (is that every DBA's lament?). I haven't created the Archive instance VG yet. I have carved the luns for it out of the EVA (placeholder). Did that before another Admin came along wanting to gobble the minimum required space up.

This experience will remind me that, when I do create the VG for archive DB it will be with a much larger Max PV value AND Max LV value than the default of 16.

Guess we learned me something, huh?