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When undertaking a project to consolidate servers through virtualization, you typically find under-
utilized resources on the bare-metal server; however, storage tends to be over-allocated. Now,
XenServer’s resource virtualization approach means that storage can also be consolidated in clusters;
moreover, thin provisioning can be selected to optimize storage utilization.
As your storage needs grow, you can add storage nodes to increase performance and capacity – a
single, simple GUI operation is all that is required to add a new node to a management group and
storage cluster. HP SAN/iQ storage software automatically redistributes your data based on the new
cluster size, immediately providing additional space to support the growth of thinly-provisioned
volumes. There is no need to change VM configurations or disrupt access to live data volumes.
However, there is a risk associated with the use of thin provisioning. Since less space is reserved on
the SAN than that presented to XenServer hosts, writes to a thinly-provisioned volume may fail if the
SAN should run out of space. To minimize this risk, SAN/iQ software monitors utilization and issues
warnings when a cluster is nearly full, allowing you to plan your data growth needs in conjunction
with thin provisioning. Thus, to support planned storage growth, it is a best practice to configure e-
mail alerts, Simple Network Management Protocol (SNMP) triggers, or CMC storage monitoring so
that you can initiate an effective response prior to a full-cluster event. Should a full-cluster event occur,
writes requiring additional space cannot be accepted and will fail until such space is made available,
effectively forcing the SR offline.
In order to increase available space in a storage cluster, you have the following options:
Add another storage node to the SAN
Delete other volumes
Reduce the volume replication level
Note
Reducing the replication level or omitting replication frees up space;
however, the affected volumes would become more prone to failure.
Replicate volumes to another cluster and then delete the originals
Note
After moving volumes to another cluster, you would have to reconfigure
XenServer host access to match the new SR.
Adding a storage node to a cluster may be the least disruptive option for increasing space without
impacting data availability.
This section has provided guidelines and best practices for configuring a new iSCSI volume. The
following section describes how to configure a XenServer host.
Configuring a XenServer Host
This section provides guidelines and best practices for configuring a XenServer host so that it can
communicate with an HP StorageWorks P4000 SAN, ensuring that the storage bandwidth for each
VM is optimized. For example, since XenServer iSCSI SRs depend on the underlying network
configuration, you can maximize availability by bonding network interfaces; in addition, you can
create a dedicated storage network to achieve predictable storage throughput for VMs. After you
