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

[Gianluca Cecchi]

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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