[ovirt-users] Behaviour when attaching shared iSCSI storage with existing data

[Doron Fediuck]

On 9 January 2018 at 13:54, Yaniv Kaul <ykaul at redhat.com> wrote:

>
>
> On Mon, Jan 8, 2018 at 11:52 PM, Sam McLeod <mailinglists at smcleod.net>
> wrote:
>
>> Hi Yaniv,
>>
>> Thanks for your detailed reply, it's very much appreciated.
>>
>> On 5 Jan 2018, at 8:34 pm, Yaniv Kaul <ykaul at redhat.com> wrote:
>>
>> Indeed, greenfield deployment has its advantages.
>>
>>>
>>> The down side to that is juggling iSCSI LUNs, I'll have to migrate VMs
>>> on XenServer off one LUN at a time, remove that LUN from XenServer and add
>>> it to oVirt as new storage, and continue - but if it's what has to be done,
>>> we'll do it.
>>>
>>
>> The migration of VMs has three parts:
>> - VM configuration data (from name to number of CPUs, memory, etc.)
>>
>>
>> That's not too much of an issue for us, we have a pretty standard set of
>> configuration for performance / sizing.
>>
>> - Data - the disks themselves.
>>
>>
>> This is the big one, for most hosts at least the data is on a dedicated
>> logical volume, for example if it's postgresql, it would be LUKS on top of
>> a logical volume for /var/lib/pgsql etc....
>>
>> - Adjusting VM internal data (paths, boot kernel, grub?, etc.)
>>
>>
>> Everything is currently PVHVM which uses standard grub2, you could
>> literally dd any one of our VMs to a physical disk and boot it in any
>> x86/64 machine.
>>
>> The first item could be automated. Unfortunately, it was a bit of a
>> challenge to find a common automation platform. For example, we have great
>> Ansible support, which I could not find for XenServer (but[1], which may be
>> a bit limited). Perhaps if there aren't too many VMs, this could be done
>> manually. If you use Foreman, btw, then it could probably be used for both
>> to provision?
>> The 2nd - data movement could be done in at least two-three ways:
>> 1. Copy using 'dd' from LUN/LV/raw/? to a raw volume in oVirt.
>> 2. (My preferred option), copy using 'dd' from LUN/LV/raw and upload
>> using the oVirt upload API (example in Python[2]). I think that's an easy
>> to implement option and provides the flexibility to copy from pretty much
>> any source to oVirt.
>>
>>
>> A key thing here would be how quickly the oVirt API can ingest the data,
>> our storage LUNs are 100% SSD each LUN can easily provide at least 1000MB/s
>> and around 2M 4k write IOP/s and 2-4M 4k read IOP/s so we always find
>> hypervisors disk virtualisation mechanisms to be the bottleneck - but
>> adding an API to the mix, especially one that is single threaded (if that
>> does the data stream processing) could be a big performance problem.
>>
>
> Well, it's just for the data copy. We can do ~300 or so MBps in a single
> upload API call, but you can copy multiple disks via multiple hypervisors
> in parallel. In addition, if you are using 'dd' you might even be able to
> use sg_xcopy (if it's the same storage) - worth looking into it.
> In any case, we have concrete plans to improve the performance of the
> upload API.
>
>>
>> 3. There are ways to convert XVA to qcow2 - I saw some references on the
>> Internet, never tried any.
>>
>>
>> This is something I was thinking of potentially doing, I can actually
>> export each VM as an OVF/OVA package - since that's very standard I'm
>> assuming oVirt can likely import them and convert to qcow2 or raw/LVM?
>>
>
> Well, in theory, OVF/OVA is a standard. In practice, it's far from it - it
> defines how the XML should look and what it contains, but a VMware
> para-virtual NIC is not a para-virtual Xen NIC is not an oVirt
> para-virtual NIC, so the fact it describes a NIC means nothing when it
> comes to cross-platform compatibility.
>
>
While exporting, please ensure you include snapshots. You can learn more on
snapshot tree export support in Xen here:
https://xenserver.org/partners/18-sdk-development/114-import-export-vdi.html


>
>>
>> As for the last item, I'm really not sure what changes are needed, if at
>> all. I don't know the disk convention, for example (/dev/sd* for SCSI disk
>> -> virtio-scsi, but are there are other device types?)
>>
>>
>> Xen's virtual disks are all /dev/xvd[a-z]
>> Thankfully, we partition everything as LVM and partitions (other than
>> boot I think) are mounted as such.
>>
>
> And there's nothing that needs to address such path as /dev/xvd* ?
> Y.
>
>
>
>>
>>
>> I'd be happy to help with any adjustment needed for the Python script
>> below.
>>
>>
>> Very much appreciated, when I get to the point where I'm happy with the
>> basic architectural design and POC deployment of oVirt - that's when I'll
>> be testing importing VMs / data in various ways and have made note of these
>> scripts.
>>
>>
>> Y.
>>
>> [1] http://docs.ansible.com/ansible/latest/xenserver_facts_module.html
>> [2] https://github.com/oVirt/ovirt-engine-sdk/blob/master/sd
>> k/examples/upload_disk.py
>>
>>
>>
>>
>
> _______________________________________________
> Users mailing list
> Users at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ovirt.org/pipermail/users/attachments/20180109/e38311ee/attachment.html>