Discussion:
best way to use rbd device in (libvirt/qemu)
(too old to reply)
Marc Roos
2018-02-08 09:19:32 UTC
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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
used?
- 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'
function='0x0'/>
</disk>

2. direct
<disk type='network' device='disk'>
<driver name='qemu' type='raw' cache='writeback'/>
<auth username='rbd.vps'>
<secret type='ceph'
uuid='9b185c64-8ca2-4e5e-b566-fb8a56b87e2c'/>
</auth>
<source protocol='rbd' name='rbd/vps-test2'>
<host name='192.168.10.111' port='6789'/>
<host name='192.168.10.112' port='6789'/>
<host name='192.168.10.113' port='6789'/>
</source>
<target dev='sda' bus='scsi'/>
<boot order='1'/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</disk>

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