HPP Enterprises P4000 SAN - Manual (Page 51)

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Figure 45. Reattach storage repositories
Once the volume is reattached, a VM needs to be created of the same type and reattached to the
virtual disk on that storage repository. Create a new VM, select the appropriate operating system
template, provide the appropriate name. The Virtual Disks option may select anything as this will need
to be manually changed. Do not select starting the VM automatically as changes still need to occur.
Highlight the VM and select the storage tab. Detach the current virtual disk (incorrectly chosen
earlier) and select attach. Select the XPSP2-05 SR and virtual disk on that SR volume. Note that (No
Name) is the default on a reattach and may be changed to “0” as to XenServer defaults. The Virtual
Disk name is changed on the Storage tab, properties for the XPSP2-05 SR. Select Attach. The VM
may now be started from the state as stored on the SR. Note that SR, virtual disk, and VM uniqueness
will be addressed later in this document and the requirements here specify that no cloned XPSP2-05
image exists in the resource pool or any other XenServer host seen by XenCenter.
Virtual Machines (VMs)
Creating VMs
Once storage repositories have been created for a XenServer host or resource pool, a virtual machine
may be created and installed on the storage repository. It is suggested best practice to name the
operating system with the same name as the storage repository as well as the iSCSI volume. In this
manner, it is clear which VM is contained within which virtual disk on a storage repository stored on
which iSCSI volume.
In planning for VM Storage Repository use, certain best practices must be followed for iSCSI LVM
supported volumes. An LVM over iSCSI volume may contain many virtual disks; however, it is
considered best practice and best performance to allocate a single storage repository to a single
virtual machine. Multiple virtual disks on a single storage repository allocated to a single virtual
machine is also acceptable. In a XenServer resource pool, utilizing shared storage, each XenServer
host in the pool establishes an active session to the shared storage, if multiple VMs were stored on a
single storage repository and each VM could be run by a different XenServer host. With HP
StorageWorks P4000 clustered storage, in order to preserve volume integrity across multiple initiators
to the same volume, a volume lock for writes occurs allowing only a single initiator to write at a time
and thereby preserving time sequenced writes amongst multiple initiators sharing the storage. A
performance bottleneck can therefore occur, which results in the recommendation for a single
XenServer host to write to a single storage repository at a time. In order to enforce this best practice
recommendation, a single virtual machine must be installed to a single storage repository.
Size of the storage repository
Size of the storage repository is dependent upon several factors including: size of the VM virtual disk
allocated for the operating system, applications, XenCenter snapshot requirements either from the