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

On Mon, Jan 8, 2018 at 11:52 PM, Sam McLeod <mailinglists(a)smcleod.net&gt; wrote: > Hi Yaniv, > > Thanks for your detailed reply, it's very much appreciated. > > On 5 Jan 2018, at 8:34 pm, Yaniv Kaul <ykaul(a)redhat.com&gt; 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.

> > 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(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/users