[fedora-virt] Virtual Disk Setup

Rich Mahn rich at lat.com
Wed Jul 15 15:56:56 UTC 2009


> > 1. Each f11 VM needs three file systems--/boot, root, and swap
> >    (assuming you can call swap a file system).  Is it better to create
> >    three LVs (each) on the hosts, and treat it as three separate disks
> >    on the VMs?  Or is it better to just create one LV on the host and
> >    then divide up that virtual disk on the VM?
> There's no point separating /boot & root onto separate virtual
> disks. You could argue there's a possible advatnage in having
> swap separate if you expect to use swap in the guest, and you
> have separate disk spindles in the host you could dedicate to 
> the guest' swap disk. To be honest though this is niche benefit
> at best.
> THe only separation I'd do is for the OS system disks, vs application
> data disks (or /home if you intended to store lots of data there).
> this makes it easier to upgrade OS - eg provision a new OS with the
> latest disto, and then just move your data disk to the new guest ,
> and throw away the old guest.

Yes.  I planned on doing a bit of this anyhow.  Testing some applications
under different configuration and the like.

> > 2. Do I get better performance/stability by NOT using lvm on the VMs?
> >    In other words, just partition the virtio disk and create
> >    filesystems directly on the partitions?  Or do the wonders of LVM
> >    and virtio already build in any advantage that might give?
> LVM makes is easier to resize guest FS. eg add a second disk
> to the guest, format it as a LVM PV and add it to your VG.
> That's pretty much only wayto add more capacity on a running
> guest.

I hadn't thought about that.  With abundant disk space on the host,
I can also make the second disk large enough to migrate the first
PV on the VM to the second, remove the first pv, and then still
only use one LV from the host.


> > 4. Lastly (for now) are these issues too miniscule in their effects
> >    that I probably shouldn't even be worrying about them?
> That's certainly my opinion. Sure you get some performance
> but you loose the great administrative flexibility  of LVM.
> Daniel

Sounds good.  Thanks for your help.


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