Den fre 21 aug. 2020 kl 23:46 skrev 差很多先生 <948355199@qq.com>:
Hello Cephers, I am a newcomer to Ceph.I know that RBD is a distributed block storage device and libvirt supports rbd pool type. Suppose I have a ceph cluster and use it to build a rbd pool to store virtual machine images. When multiple qemu-kvm clients use the image in the rbd pool to start virtual machines at the same time, will rbd perform load balancing? That is, different hosts in the cluster would send images to different clients at the same time. Or only one host will send images, and the other hosts will only send images when the current host is down? Would someone explain it to me please?
The 40G image you create in qemu-kvm will be split into 4M pieces, so this will become some 10000 pieces. If this qemu guest reads the virtual "harddrive" from 0 -> 39.99G it will in total send 10k requests at 4M each, and each of these 10k pieces will end up on a (pseudo)random PG, so the IO load will be spread to all involved OSDs for your RBD image. Same for all other qemu VMs and their drives on the same or other qemu-kvm hosts. This is how you can get more total IO perf by adding more osd hosts and more drives to your cluster. -- May the most significant bit of your life be positive.