best way to use rbd device in (libvirt/qemu)
(too old to reply)
Marc Roos
2018-02-08 09:19:32 UTC
Afaik you can configure the use of an rbd device like below.

- Am I correct in assuming that the first one is not recommended because
it can use some caching? (I thought I noticed a speed difference between
these 2, and assumed it was related to caching).
- I guess in both cases the kernel module is used and same libraries are
- Are there any other (dis)advantages?

1. via mapped rbd device
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='writeback'/>
<source dev='/dev/rbd/rbd/vps-test2'/>
<target dev='vda' bus='virtio'/>
<boot order='2'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0c'

2. direct
<disk type='network' device='disk'>
<driver name='qemu' type='raw' cache='writeback'/>
<auth username='rbd.vps'>
<secret type='ceph'
<source protocol='rbd' name='rbd/vps-test2'>
<host name='' port='6789'/>
<host name='' port='6789'/>
<host name='' port='6789'/>
<target dev='sda' bus='scsi'/>
<boot order='1'/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>