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Chapter 14. Working With Storage
130
VMware
vSphere
Citrix
XenServer
KVM Oracle VM
Fiber Channel support VMFS Yes, via
Existing SR
Yes, via
Shared
Mountpoint
No
NFS support Y Y Y Y
Local storage support Y Y Y Y
Storage over-provisioning NFS and
iSCSI
NFS NFS No
XenServer uses a clustered LVM system to store VM images on iSCSI and Fiber Channel volumes
and does not support over-provisioning in the hypervisor. The storage server itself, however, can
support thin-provisioning. As a result the CloudPlatform can still support storage over-provisioning by
running on thin-provisioned storage volumes.
KVM supports "Shared Mountpoint" storage. A shared mountpoint is a file system path local to each
server in a given cluster. The path must be the same across all Hosts in the cluster, for example /mnt/
primary1. This shared mountpoint is assumed to be a clustered filesystem such as OCFS2. In this
case the CloudPlatform does not attempt to mount or unmount the storage as is done with NFS. The
CloudPlatform requires that the administrator insure that the storage is available
Oracle VM supports both iSCSI and NFS storage. When iSCSI is used with OVM, the CloudPlatform
administrator is responsible for setting up iSCSI on the host, including re-mounting the storage after
the host recovers from a failure such as a network outage. With other hypervisors, CloudPlatform
takes care of mounting the iSCSI target on the host whenever it discovers a connection with an iSCSI
server and unmounting the target when it discovers the connection is down.
With NFS storage, CloudPlatform manages the overprovisioning. In this case the global configuration
parameter storage.overprovisioning.factor controls the degree of overprovisioning. This is independent
of hypervisor type.
Local storage is an option for primary storage for vSphere, XenServer, Oracle VM, and KVM.
When the local disk option is enabled, a local disk storage pool is automatically created on each
host. To use local storage for the System Virtual Machines (such as the Virtual Router), set
system.vm.use.local.storage to true in global configuration.
CloudPlatform supports multiple primary storage pools in a Cluster. For example, you could provision
2 NFS servers in primary storage. Or you could provision 1 iSCSI LUN initially and then add a second
iSCSI LUN when the first approaches capacity.
14.2.4. Storage Tags
Storage may be "tagged". A tag is a text string attribute associated with primary storage, a Disk
Offering, or a Service Offering. Tags allow administrators to provide additional information about the
storage. For example, that is a "SSD" or it is "slow". Tags are not interpreted by CloudPlatform. They
are matched against tags placed on service and disk offerings. CloudPlatform requires all tags on
service and disk offerings to exist on the primary storage before it allocates root or data disks on the
primary storage. Service and disk offering tags are used to identify the requirements of the storage
that those offerings have. For example, the high end service offering may require "fast" for its root disk
volume.
The interaction between tags, allocation, and volume copying across clusters and pods can be
complex. To simplify the situation, use the same set of tags on the primary storage for all clusters in
a pod. Even if different devices are used to present those tags, the set of exposed tags can be the
same.