Designing Disaster Tolerant High Availability Clusters, 10th Edition, March 2003 (B7660-90013)

Building an Extended Distance Cluster Using MC/ServiceGuard
Two Data Centers and Third Location Architectures
Chapter 2 59
• Fibre Channel Arbitrated loops are limited to a maximum of four
nodes and nine Fibre Channel Disk Arrays per loop. This restriction
does not exist if Direct Fabric Attach configurations are used.
• Any combination of the following Fibre Channel capable disk arrays
may be used: Model FC30, HP StorageWorks FC10, HP
StorageWorks FC60, HP StorageWorks Virtual Arrays, HP
StorageWorks Disk Array XP or EMC Symmetrix Disk Arrays.
• Application data must be mirrored between the primary data
centers. If MirrorDisk/UX is used, Mirror Write Cache (MWC) must
be the Consistency Recovery policy defined for all mirrored logical
volumes. This will allow for resynchronization of stale extents after
a failure of a mirror copy, rather than requiring a full
resynchronization. You must ensure that the mirror copies reside in
different data centers, so it is recommended to configure physical
volume groups for the disk devices in each data center, and to use
Group Allocation Policy for all mirrored logical volumes.
• Due to the maximum of 3 disk images (one original and two mirror
copies) allowed in MirrorDisk/UX, if JBODs are used for application
data, only one data center can contain JBODs while the other data
center must contain disk arrays with hardware mirroring.
• VERITAS Volume Manager (VxVM) mirroring is supported for
clusters of 2 or 4 nodes. However, the cluster lock devices must still
be configured in LVM Volume Groups. The maximum distance
supported for VxVM is 10 kilometers. You must ensure that the
mirror copies reside in different data centers, and the DRL (Dirty
Region Logging) feature must be used. Raid 5 mirrors are not
supported.
• VERITAS Cluster Volume Manager (CVM) mirroring is supported
for MC/ServiceGuard or ServiceGuard OPS Edition clusters
containing 2 or 4 nodes. In CVM configurations Arbitrator nodes are
not supported, and a Quorum Server node must be used instead.