RBD-storage

The virtual disk of a virtual machine is the HDD image. Virtual disks are stored in a local or network storage. RBD is a network storage which is a distributed file system designed to provide excellent reliability.  For more information please refer to the article Network storages.

Installation

1. Install Ceph:

   rpm --import 'https://ceph.com/git/?p=ceph.git;a=blob_plain;f=keys/release.asc'
   rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
   yum install snappy leveldb gdisk python-argparse gperftools-libs
   rpm -Uvh http://ceph.com/rpm-cuttlefish/el6/noarch/ceph-release-1-0.el6.noarch.rpm
   yum install ceph

2. Install the plug-in YUM Priorities (for QEMU installation from the Ceph repository):

   yum install yum-plugin-priorities

3. Enable the plug-in the configuration file /etc/yum/pluginconf.d/priorities.conf:

   [main]
   enabled = 1

4. Create the file /etc/yum.repos.d/ceph-qemu.repo with the following contents:

   [ceph-qemu]
   name=Ceph Packages for QEMU
   baseurl=http://ceph.com/packages/ceph-extras/rpm/rhel6/$basearch
   enabled=1
   priority=2
   gpgcheck=1
   type=rpm-md
   gpgkey=https://ceph.com/git/?p=ceph.git;a=blob_plain;f=keys/release.asc
   
   [ceph-qemu-noarch]
   name=Ceph QEMU noarch
   baseurl=http://ceph.com/packages/ceph-extras/rpm/rhel6/noarch
   enabled=1
   priority=2
   gpgcheck=1
   type=rpm-md
   gpgkey=https://ceph.com/git/?p=ceph.git;a=blob_plain;f=keys/release.asc
   
   [ceph-qemu-source]
   name=Ceph QEMU Sources
   baseurl=http://ceph.com/packages/ceph-extras/rpm/rhel6/SRPMS
   enabled=1
   priority=2
   gpgcheck=1
   type=rpm-md
   gpgkey=https://ceph.com/git/?p=ceph.git;a=blob_plain;f=keys/release.asc

5. Install QEMU from Ceph:

   yum update
   yum install qemu-img qemu-kvm qemu-kvm-tools

How VMmanager works with RBD-storage

When creating the RBD-storage VMmanager is trying to find the ceph cluster monitor specified on the cluster creation form using the key that is normally located in /usr/local/mgr5/etc/ssh_id_rsa. Then VMmanager performs the following operations:

1. Adds the storage with the same name as in VMmanager:

   ceph osd pool create <Storage_name> 128 128

2. Checks/adds a ceph user-client (the client name is specified by the CephAuthUserName parameter in the vmmgr.conf configuration file, the default value is vmmgr):

   ceph auth get-or-create client.<client_name> mon 'allow r' osd 'allow class-read object_prefix rbd_children, allow rwx pool=<storage_name>'

3. Creates a "secret" in libvirt and adds the above key.
4. Defines a list of cluster monitors and specifies it into the rbdmonitor table of the database.

When adding a new hard drive image in the RBD-storage, VMmanager connects via ssh to the first monitor of the cluster and executes the command

qemu-img create -f rbd rbd:<storage_name>/<Image_name> 2G

Execute the command when deleting the disk:

rbd -p <storage_name> rm <Image_name>