Number of volume groups on a disk 1

[SpiritOfLennon]

Hi,
I'm planning a disk mirror strategy on HP-UX 11. Is it correct that you can only define one volume per physical disk using LVM?
Thanks


SOL
I'm only guessing but my guess work generally works for me.

 

[yai]

Hi,
you can put one disk in exactly one volume group. You can create any number of logical volumes in a volume group.
And remember:
- you cannot mirror disks with MirrorDisk-UX (the name is misleading) you can only mirror logical volumes.
- try to mirror from one disk to another ;-)
- if you mirror the system disk (vg00), first mirror lvol3 (mounted on /), so you can boot from it.
- if you set up new lvols, use the following procedure
1. create lvol with 0 extends
2. mirror the lvol
3. extend the lvol to the number of extends you need
otherwise the mirroring process will take some time, because LVM physically copies all extends to the mirror.

 

[SpiritOfLennon]

Thanks for that. Sorry I did mean volume groups.

You say you can put one disk in exactly one volume group.

Does that mean I can't put more than one volume group on a one disk?

SOL
I'm only guessing but my guess work generally works for me.

 

[yai]

yep.
one disk in one vg. many disks in one vg. many lvols in one vg, and you can control on which disk inside the vg.
Actually, there is a section called vgra (volume group reserved area) on each disk which has room for one vgid (volume group id) and some space for each logical volume in this vg, so my comment above ("any number of lvols") is not correct. The number is limited by the vgra size which in turn is created using the max_lv and max_pv parameters you specify when vgcreate#ing the vg.
Why do you want to put more than one vg one one disk?

 

[SpiritOfLennon]

I have a server with three small volume groups and the IT manager of the site has bought a giant disk which he wanted to mirro the three volume groups to. I guess he can't do this then?

SOL
I'm only guessing but my guess work generally works for me.

 

[yai]

IT managers ...
I suppose you CAN'T do it. Or better: I suppose you can, but it's not supported. The way to do it is to slice the big disk, so the OS sees it as many disks. You can then add each single disk (slice) to another vg. But, as i said, i don't think it's supported. And i never sliced disks on HPUX, so i can't help you any further.
I don't know if there is any reason for the 3 small vgs. Best thing would be to migrate them all into one vg and then add the big disk as a mirror for the rest.