I thought we were leaning toward the option where nova itself doesn't impose a limit, but lets the virt driver decide.
I would really like NOT to see logic like this in any nova code: > if kvm|qemu: > return 256 > elif POWER: > return 4000 > elif: > ... On 06/11/2018 10:06 AM, Kashyap Chamarthy wrote: > On Mon, Jun 11, 2018 at 11:55:29AM +0200, Sahid Orentino Ferdjaoui wrote: >> On Fri, Jun 08, 2018 at 11:35:45AM +0200, Kashyap Chamarthy wrote: >>> On Thu, Jun 07, 2018 at 01:07:48PM -0500, Matt Riedemann wrote: > > [...] > >>>> The 26 volumes thing is a libvirt driver restriction. >>> >>> The original limitation of 26 disks was because at that time there was >>> no 'virtio-scsi'. >>> >>> (With 'virtio-scsi', each of its controller allows upto 256 targets, and >>> each target can use any LUN (Logical Unit Number) from 0 to 16383 >>> (inclusive). Therefore, the maxium allowable disks on a single >>> 'virtio-scsi' controller is 256 * 16384 == 4194304.) Source[1]. >> >> Not totally true for Nova. Nova handles one virtio-scsi controller per >> guest and plug all the volumes in one target so in theory that would >> be 16384 LUN (only). > > Yeah, I could've been clearer that I was only talking the maximum > allowable disks regardless of how Nova handles it. > >> But you made a good point the 26 volumes thing is not a libvirt driver >> restriction. For example the QEMU SCSI native implementation handles >> 256 disks. >> >> About the virtio-blk limitation I made the same finding but Tsuyoshi >> Nagata shared an interesting point saying that virtio-blk is not longer >> limited by the number of PCI slot available. That in recent kernel and >> QEMU version [0]. >> >> I could join what you are suggesting at the bottom and fix the limit >> to 256 disks. > > Right, that's for KVM-based hypervisors. > > Eric Fried on IRC said the other day that for IBM POWER hypervisor they > have tested (not with OpenStack) upto 4000 disks. But I am yet to see > any more concrete details from POWER hypervisor users on this thread. > > If people can't seem to reach an agreement on the limits, we may have to > settle with conditionals: > > if kvm|qemu: > return 256 > elif POWER: > return 4000 > elif: > ... > > Before that we need concrete data that it is a _reasonble_ limit for > POWER hypervisor (and possibly others). > >> [0] >> https://review.openstack.org/#/c/567472/16/nova/virt/libvirt/blockinfo.py@162 > > [...] > __________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
