HPP Enterprises P4000 SAN - Manual (Page 52)

52
console or from VSS enabled requestors, location of additional application data and logs (within
XenServer virtual disks or separate iSCSI volumes), and planning for future growth.
An operating system installation size depends upon features chosen during the installation as well as
temporary file space. Additional applications installed will also occupy space and are dependent
upon what the VM applications are intended to run. Applications may also rely upon data and
logging space to be available. Depending upon the architecture of a solution, separate iSCSI volumes
may also be implemented for VM data stores that are mapped directly within the VM rather than
externally thru the XenServer host as a storage repository. An LVM over iSCSI volume is formatted as
an LVM volume virtual disk space on the LVM volume which has little overhead occupied by the LVM
file system.
Snapshots require space on the original storage repository during creation. Although initially not
occupying much space, changes to the original virtual disk volume over time may force the snapshot
to occupy as much space as the original volume. Also, in order to utilize a snapshot, the original VM
virtual disk volume space must also be available on the same storage repository to create a VM from
that snapshot. In order to keep a best practice configuration, a VM created from a snapshot should
then be copied to a new storage repository. This same approach will apply to VSS created snapshots.
Planning for a VM must also take into consideration if snapshot features are to leave available space
for snapshots or VM creations from snapshots.
Planning for future growth also minimizes the amount of administration that must occur to
accommodate VM file space growth. Since HP StorageWorks iSCSI volumes can be created as Thinly
Provisioned volumes, a larger storage repository than initially needed may be created and a larger
virtual disk allocated to a VM than initially needed. The unused space is not carved out of the iSCSI
virtualization space as the configuration is only passed down as a larger volume. By provisioning a
larger than needed volume, the administrator may be able to prolong changing storage allocations
and thereby save future administrative actions and thereby save time.
Increasing storage repository volume size
HP StorageWorks P4000 volumes may be edited at any time and volume size increased to
accommodate future needs. In order to have an increase in volume size be recognized by XenServer
hosts and ultimately VMs, several procedures must be performed. In the HP StorageWorks CMC,
highlight the volume, right click on the volume and chose Edit Volume. Change the Size from the
current size to the new larger size. In this example, 10GB is changed to 50GB. From the storage
perspective, the volume is now larger, however, it needs to be recognized from the XenServer host. In
the XenCenter console, ensure that any VM which consists of virtual disks stored on that storage
repository is shut down. The storage repository must be logged out and re-logged in at the iSCSI
layer to recognize the newly available storage. With the storage repository highlighted, right click on
the repository and select Detach Storage Repository. Select yes to detach the repository and make the
virtual disks inaccessible. Note that storage repository disk icon will become grey and the state will
be detached. Viewing the iSCSI Sessions from within the CMC will note that the sessions will be
logged out. In the XenCenter console with the storage repository highlight, right click and select
Reattach Storage Repository. Keep the same name of the Storage Repository; enter the same target
host of the iSCSI VIP target portal. Select Discover IQNs and select the same iSCSI volume that was
previously detached. Select Discover LUNs and Finish. A warning will request that you ensure that
you wish to reattach the SR, select Yes. The iSCSI volume will re-establish iSCSI sessions to all
XenServer hosts in the resource pool. The reattached storage repository will now make the extra
allocated space available. This space may now be used for snapshots or additional virtual disks.
VMs are allocated virtual disks. To grow a virtual disk, in the XenCenter console, highlight the newly
expanded storage repository. Select the storage tab. Highlight the “0” virtual disk and select
properties. Select the Size and Location property and increase the size allocation. In this example, a