I am using the cinder-lvm backend right now and performance is quite good. My situation is similar without the migration parts. Prior to this arrangement I was using iscsi to mount a disk in /var/lib/nova/instances and that also worked quite well.

If you don't mind me asking, what kind of i/o performance are you looking for?

On Fri, Aug 2, 2019 at 12:25 PM Budai Laszlo <laszlo.budai@gmail.com> wrote:

Thank you Daniel,

My colleague found the same solution in the meantime. And that helped us as well.

Kind regards,
Laszlo

On 8/2/19 6:50 PM, Daniel Speichert wrote:
> For the case of simply using local disk mounted for /var/lib/nova and raw disk image type, you could try adding to nova.conf:
>
> preallocate_images = space
>
> This implicitly changes the I/O method in libvirt from "threads" to "native", which in my case improved performance a lot (10 times) and generally is the best performance I could get.
>
> Best Regards
> Daniel
>
> On 8/2/2019 10:53, Budai Laszlo wrote:
>> Hello all,
>>
>> we have a problem with the performance of the disk IO in a KVM instance.
>> We are trying to provision VMs with high performance SSDs. we have investigated different possibilities with different results ...
>>
>> 1. configure Nova to use local LVM storage (images_types = lvm) - provided the best performance, but we could not migrate our instances (seems to be a bug).
>> 2. use cinder with lvm backend and instance locality, we could migrate the instances, but the performance is less than half of the previous case
>> 3. mount the ssd on /var/lib/nova/instances and use the images_type = raw in nova. We could migrate, but the write performance dropped to ~20% of the images_types = lvm performance and read performance is ~65% of the lvm case.
>>
>> do you have any idea to improve the performance for any of the cases 2 or 3 which allows migration.
>>
>> Kind regards,
>> Laszlo
>>