9.5.01 HP P4000 SAN Solution User Guide (AX696-96168, February 2012)

How data protection levels work
The system calculates the actual amount of storage resources needed for all data protection levels.
When you choose Network RAID-10, Network RAID-10+1, or Network RAID-10+2, data is striped
and mirrored across either two, three, or four adjacent storage systems in the cluster.
When you choose Network RAID-5 or Network RAID-6, the layout of the data stripe, including
parity, depends on both the Network RAID mode and cluster size. These Network RAID stripes are
rotated across the storage cluster to support configurations where the number of storage systems
in the cluster is larger than the Network RAID stripe. When using Network RAID 5, the Network
RAID stripe spans three to five storage systems including single parity. When using Network RAID
6, the Network RAID stripe spans five to seven storage systems including dual parity.
CAUTION: A management group with two storage systems and a Failover Manager is the
minimum configuration for automated fault tolerant operation. Although the SAN/iQ software
allows you to configure Network RAID-10 on two storage systems, this does not guarantee data
availability in the event that one storage system becomes unavailable, due to the communication
requirements between managers. See “Managers overview” (page 107).
CAUTION: Any volume with Network RAID-0 is not protected from complete system failure or
reboot.
Network RAID-10 (2–Way Mirror)
Network RAID-10 data is striped and mirrored across two storage systems. Network RAID-10 is
the default data protection level assigned when creating a volume, as long as there are two or
more storage systems in the cluster. Data in a volume configured with Network RAID-10 is available
and preserved in the event that one storage system becomes unavailable.
Network RAID-10 is generally the best choice for applications that write to the volume frequently
and don't need to tolerate multiple storage system failures. Such applications include databases,
email, and server virtualization. Network RAID-10 is also good for Multi-Site SANs. Using Network
RAID-10 in a Multi-Site SAN ensures that data remains available in the event that one site becomes
unavailable. However, if one site does go down, the Network RAID-10 volumes are then not
protected from complete system failure or reboot.
Figure 58 (page 144) illustrates the write patterns on a cluster with four storage systems configured
for Network RAID-10.
Figure 58 Write patterns in Network RAID-10 (2–Way Mirror)
Network RAID-10+1 (3-Way Mirror)
Network RAID-10+1 data is striped and mirrored across three or more storage systems. Data in
a volume configured with Network RAID-10+1 is available and preserved in the event that any
two storage systems become unavailable.
144 Provisioning storage