Hi, I think that https://wiki.mikejung.biz/KVM_/_Xen might be quite useful Pretty much there won’t be a universal recipe but rather combination of what are kernel/QEMU/OpenStack… versions and implementation choices that were made -Guest OS/host OS kernel version -QEMU version -OpenStack release. Basically the part of XML definition of disk is controlled by OpenStack -virtio_blk vs. some fully-virtualized stuff like ide is used -the backend for virtual disk
some points possibly to add to that article: 1) For virtio_scsi in OpenStack see https://blueprints.launchpad.net/nova/+spec/cinder-backend-report-discard 2) Linux itself is supposed to detect if it works on HDD or SSD See: smartctl -a /dev/sd<x> and cat /sys/block/sd<x>/queue/rotational (0 –SSD, 1 – HDD) But results might be contradictory/interpretation of that is not straightforward. Maybe someone has better insight, but what I understood from one hand not all SSD drives report to being as such And that’s why sysfs entry /sys/block/sd<x>/queue/rotational was introduced which was meant to enforce ‘SSD-like behavior) https://lwn.net/Articles/408428/ But then I kinda understood that Linux might/is supposed to set it correctly (via udev rules?) But it should be noted in Ubuntu 12.04/Ubuntu 14.04 that I worked with that had SSDs this flag /rotational was ‘1’ on SSD, ie. Incorrect…) 3) The question of cfq vs. deadline vs. noop scheduler (apparently both in guest and host) where decision should be based on workloads/recommendations of OS vendor (/which again might be release-dependent). BR. Konstantin From: Tim Bell [mailto:[email protected]] Sent: Friday, August 05, 2016 12:44 PM To: openstack-operators <[email protected]> Subject: [Openstack-operators] Tuning I/O with SSDs Has anyone a good recipe for improving I/O performance when the hypervisor has SSDs ? The configuration is CentOS 7 for guest and hypervisor with KVM. Tim
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