On Tue, Jul 11, 2017 at 3:14 PM, Gianluca Cecchi <gianluca.cecchi@gmail.com> wrote:

On Tue, Jul 11, 2017 at 2:59 PM, Gianluca Cecchi <gianluca.cecchi@gmail.com> wrote:

Hello,

I have a source oVirt environment with storage domain on FC

I have a destination oVirt environment with storage domain on iSCSI

The two environments can communicate only via the network of their respective hypervisors.

The source environment, in particular, is almost isolated and I cannot attach an export domain to it or something similar.

So I'm going to plan a direct move through dd of the disks of some VMs

The workflow would be

On destination create a new VM with same config and same number of disks of the same size of corresponding source ones.

Also I think same allocation policy (thin provision vs preallocated)

Using lvs -o+lv_tags I can detect the names of my origin and destination LVs, corresponding to the disks

When a VM is powered down, the LV that maps the disk will be not open, so I have to force its activation (both on source and on destination)

lvchange --config 'global {use_lvmetad=0}' -ay vgname/lvname

copy source disk with dd through network (I use gzip to limit network usage basically...)

on src_host:

dd if=/dev/src_vg/src_lv bs=1024k | gzip | ssh dest_host "gunzip | dd bs=1024k of=/dev/dest_vg/dest_lv"

deactivate LVs on source and dest

lvchange --config 'global {use_lvmetad=0}' -an vgname/lvname

Try to power on the VM on destination

Some questions:

- about overall workflow

- about dd flags, in particular if source disks are thin vs preallocated

Thanks,

Gianluca

Some further comments:

- probably better/safe to use SPM hosts for lvchange commands both on source and target, as this imply metadata manipulation, correct?

- when disks are preallocated, no problems, but when they are thin, I can be in this situation

source disk defined as 90Gb disk and during time it has expanded up to 50Gb

dest disk at the beginning just after creation will normally be of few GB (eg 4Gb), so the dd command will fail when fulll...

Does this mean that it will be better to create dest disk as preallocated anyway or is it safe to run 

lvextend -L+50G dest_vg/dest_lv

from command line?

Will oVirt recognize its actual size or what?

So I've done, both for thin provisioned (without having done snapshot on them, see below) and preallocated disks, and it seems to work, at least booting an OS boot disk copied over this way.

I have one further doubt.

For a VM I have a disk defined as thin provisioned and 90Gb in size.

Some weeks ago I created a snapshot for it.

Now, before copying over the LV, I have delete this snapshot.

But I see that at the end of the process, the size of the LV backing the VM disk is now actually 92Gb, so I presume that my dd over network will fail....

What could I do to cover this scenario?

What would be the command at os level in case I choose "move disk" in web admin gui to move a disk from a SD to another one?

Thanks,

Gianluca

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