[ovirt-users] Manually moving disks from FC to iSCSI

[Fred Rolland]

The move command will first create the disk structure according to the
snapshots on the destination , then a 'qemui-mg convert' will be performed
for each snapshot.

On Wed, Jul 12, 2017 at 1:31 AM, Gianluca Cecchi <gianluca.cecchi at gmail.com>
wrote:

> On Tue, Jul 11, 2017 at 3:14 PM, Gianluca Cecchi <
> gianluca.cecchi at gmail.com> wrote:
>
>>
>>
>> On Tue, Jul 11, 2017 at 2:59 PM, Gianluca Cecchi <
>> gianluca.cecchi at 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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