[Ovirt-devel] iscsi storage creation

[Scott Seago]

Justin Clacherty wrote:
> Hi,
>
> I have set up a 40GB iscsi target on my san and when I add it in to 
> the storage pool and it shows up as 40GB.  When I try to create a 40GB 
> volume in the ovirt UI it tries to but fails.  The error message is 
> that the volume will not fit.  If I create one smaller than 40GB it 
> works.  Is anyone else experiencing this?
>
> Also, if I then start a virtual machine up to install on the newly 
> created volume it sees both the smaller (39GB in this case) partition 
> and a 40GB partition (presumably the failed one).
>
> Cheers,
> Justin.
>
Hi Justin,

Ian may be able to provide a more complete answer, but there are a 
couple things  that are probably going on with the 39GB vs. 40GB size. 
First of all, if you've got a 40GB iSCSI LUN and you want to create an 
oVirt storage volume under it, we're creating a Volume Group on the LUN 
and creating Logical Volumes as storage volumes via libvirt, so the size 
available for a single LVM volume on the lun will be slightly smaller 
due to the LVM overhead.

The second issue is that while libvirt (and the oVirt DB) deal with 
storage sizes internally in KB, we're using GB in the UI at the moment 
and converting on the back end. This means for now you can only deal 
with an integral number of gigabytes. We need to do some re-thinking on 
how we handle storage and memory units -- in the above case you may have 
been able to create a 39.6GB volume (or some other value between 39 and 
40 GB).  If you really want to use the whole 40GB lun for a single VM 
you don't need to create an LVM volume -- just use the iscsi lun (shown 
in the UI as an iscsi storage volume).

As for why you see both in your VM I haven't seen that, so I'm not sure 
what would cause that -- Ian do you have any ideas on this point?

Scott