Hi Simon,
perfect! thank you!
do you find a strange issue on the snapshot of rbd? the snapshot actual size is bigger than the original image file.. if you use rbd du to check the size..
On Thu, Jan 28, 2016 at 9:44 PM, Simon Ironside <sironside@xxxxxxxxxxxxx> wrote:
On 28/01/16 12:56, Bill WONG wrote:
you dump the snapshot to raw img, possible to exprt to qcow2 format?
Yes, I dump to raw because I'm able to get better and faster compression of the image myself than using the qcow2 format.
You can export directly to qcow2 with qemu-img convert if you want:
qemu-img convert -c -p -f rbd -O qcow2 \
rbd:rbd/testvm@backup \
testvm.qcow2
and you meant create the VM using qcow2 with the local HDD storage, then
convert to rbd?
is it perfect, if you can provide more details... it's highly
appreciated.. thank you!
Ok . . .
1. Create the VM using a file-based qcow2 image then convert to rbd
# Create a VM using a regular file
virt-install --name testvm \
--ram=1024 --vcpus=1 --os-variant=rhel7 \
--controller scsi,model=virtio-scsi \
--disk path=/var/lib/libvirt/images/testvm.qcow2,size=10,bus=scsi,format=qcow2 \
--cdrom=/var/lib/libvirt/images/rhel7.iso \
--nonetworks --graphics vnc
# Complete your VM's setup then shut it down
# Convert qcow2 image to rbd
qemu-img convert -p -f qcow2 -O rbd \
/var/lib/libvirt/images/testvm.qcow2 \
rbd:rbd/testvm
# Delete the qcow2 image, don't need it anymore
rm -f /var/lib/libvirt/images/testvm.qcow2
# Update the VM definition
virsh edit testvm
# Find the <disk> section referring to your original qcow2 image
# Delete it and replace with:
<disk type='network' device='disk'>
<driver name='qemu' type='raw' discard='unmap'/>
<source protocol='rbd' name='rbd/testvm'>
<host name='ceph-mon1.example.org' port='6789'/>
<host name='ceph-mon2.example.org' port='6789'/>
<host name='ceph-mon3.example.org' port='6789'/>
</source>
<auth username='CEPH_USERNAME'>
<secret type='ceph' uuid='SECRET_UUID'/>
</auth>
<target dev='sda' bus='scsi'/>
</disk>
# Obvious use your own ceph monitor host name(s)
# Also change CEPH_USERNAME and SECRET_UUID to suit
# Restart your VM, it'll now be using ceph storage directly.
Btw, using virtio-scsi devices as above and discard='unmap' above enables TRIM support. This means you can use fstrim or mount file systems with discard inside the VM to free up unused space in the image.
2. Modify the XML produced by virt-install before the VM is started
The process here is basically the same as above, the trick is to make the disk XML change before the VM is started for the first time so that it's not necessary to shut down the VM to copy from qcow2 file to rbd image.
# Create RBD image for the VM
qemu-img create -f rbd rbd:rbd/testvm 10G
# Create a VM XML but don't start it
virt-install --name testvm \
--ram=1024 --vcpus=1 --os-variant=rhel7 \
--controller scsi,model=virtio-scsi \
--disk path=/var/lib/libvirt/images/deleteme.img,size=1,bus=scsi,format=raw \
--cdrom=/var/lib/libvirt/images/rhel7.iso \
--nonetworks --graphics vnc \
--dry-run --print-step 1 > testvm.xml
# Define the VM from XML
virsh define testvm.xml
# Update the VM definition
virsh edit testvm
# Find the <disk> section referring to your original deleteme image
# Delete it and replace it with RBD disk XML as in procedure 1.
# Restart your VM, it'll now be using ceph storage directly.
I think it's easier to understand what's going on with procedure 1 but once you're comfortable I suspect you'll end up using procedure 2, mainly because it saves having to shut down the VM and do the conversion and also because my compute nodes only have tiny local storage.
It's also possible to script much of the above with the likes of virsh detach-disk and virsh attach-device to make the disk XML change.
Cheers,
Simon.
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