RHEL Hypervisor
Hi,
Till date we use Centos + KVM as hypervisor and in that we use LVM Based raw partition for guest VM disk. And currently, we are evaluating RHEL as hypervisor with RHEVM management interface. And we use Local storage.
So currently we created lvm based partition and on top of that we formatted with file system and mounted it and then we set that mount point in RHEVM interface to use as data domain for guest VM.
So does my confusion is that, if we use formatted partition, does it make any performance impact on our guest VM ? And can we use Local disk raw partition for our guest VM in RHEVM as we before using with virt-manager and centos+kvm ?
Regards
Responses
Red Hat
Guru
7252 points
If your hypervisor systems have large internal disks, you can setup each RHEV Hypervisor in its own Cluster with "Local Storage" type Storage Domain. The guest disk images are then stored on each hypervisor local disk. However, you cannot migrate guests between hypervisors this way.
Do you have shared storage? (Fibre Channel SAN, ISCSI SAN, NFS server, or Red Hat Storage instance)
If so you don't need to present shared storage to the RHEV Manager, only to the RHEV Hypervisors.
Present the storage to the RHEV Hypervisors, but do not mount it or manually manage the storage in any way. Then use the RHEV Manager to create a Cluster with either FC, ISCSI, NFS, or POSIX type Storage Domain, and the RHEV Manager instructs the hypervisors to connect to the shared storage and create guest disks on the shared storage.
It sounds like the biggest difference for you will be allowing the RHEV Hypervisors to access and manage the storage themselves, instead of you doing it. Ideally, all you'll ever do is plug in the hypervisors and make sure they can logically access the storage, from there you drive everything from the RHEV Mananger Admin Portal.
Red Hat
Guru
7252 points
When you install the RHEV Hypervisor image, a small amount of space is used for the OS and swap, and the rest of the local disk is used for local storage and is mounted at /data/images.
For your reference, this is described in the product documentation
Red Hat
Guru
7252 points
The guest disks will be stored in a filesystem whether you allow RHEV to do it, or create a filesystem and mount it yourself.
The default filesystem type is ext4.
It's only for Fibre Channel and ISCSI type Storage Domains that guest disks are stored inside LVM Logical Volumes. The Local, NFS, and POSIX type Storage Domains use image files in the existing filesystem.
Red Hat
Guru
7252 points
Well, performance impact compared to what? :) I'd expect an enterprise SAN full of SSDs to be significantly faster than internal SATA disks. However, if you're comparing the RHEV-H image's /data/images directory to installing a RHEL Hypervisor and making an ext4 filesystem, there should be no difference between those two.
We usually see customers running their production VMs on shared storage (FC, ICSCI, NFS, POSIX) the advantage being that if the hypervisor goes down, or becomes overwhelmed, or is in maintenance for some reason then the VMs can be migrated off so those guests keep running elsewhere.
With a Local Storage Domain, if the hypervisor is down then the guest is down. This can make maintenance and capacity management harder.
Yes, using the Export Domain is one method to backup your VMs. You could run a backup agent inside the VM (which just backs up the filesystem or block devices, not the VM definition) which is no different to a backup agent inside physical systems. There are also third-party vendors like Acronis or Symantec who provide RHEV-aware backup solutions.
Automating Export Domain backup via rhevm-cli is discussed here:
RHEV VM backup and restore solution
https://access.redhat.com/site/solutions/117763
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