QLogic 10000 Series Mt. Rainier Technology Accelerates the Enterprise - Manual (Page 6)

SSG-WP12004C SN0430914-00 rev. C 11/12 6
White PaPer
When a primary fails or is otherwise unable to communicate with the other
members of a cluster, the secondary is promoted to primary, and then
assigns a new secondary, as shown in Figure 7.
Figure 7. Cluster Control Primary Failure Recovery Sequence
When the former primary comes back online and rejoins the cluster, it
learns of the new primary and secondary configuration, and then rejoins as
a regular, non-control member, as shown in Figure 8.
Figure 8. Failed Cluster Control Primary Rejoins the Cluster as Non-Control Member
independent of cluster control functions, pairs of Mt. rainier cluster
members can also cooperate to provide synchronous mirroring of cache or
SSD data LUNs. in these relationships, only one member of the pair actively
serves requests and synchronizes data to the mirror partner (that is, the
mirroring relationship is active-passive).
LUN Cache Ownership
LUN cache ownership guarantees that at any time, only one Mt. rainier is
actively caching any specified LUN. any member of an Mt. rainier cluster
that requires access to a LUN that is cached by another cluster member
redirects the i/O to the specific LUN’s cache owner, as illustrated in Figure 9.
Figure 9. LUN Cache Ownership Supporting Read Operations
in Figure 9, QLogic Mt. rainiers are installed in both servers and are
clustered together. Server 2 is then configured as the LUN cache owner for
a shared LUN. When Server 1 needs to read or write data on that shared
LUN, participation in the storage accelerator cluster tells the Mt. rainier on
Server 1 to redirect i/O to the Mt. rainier on Server 2. this i/O redirection:
• Guarantees cache coherence.
• is completely transparent to servers and applications.
• Works for both read and write caching.
• Consumes no host processor or memory resources on either server.
these characteristics are essential to the active-active clustering
applications and environments that are most critical to enterprise
information processing. Without guaranteed cache coherence, applications
such as VMware
® eSX ® clusters, Oracle ® real application Clusters (raC),
and those that rely on the Microsoft ® Windows ® Failover Clustering feature
simply cannot run with server-based SSD caching. application transparency
enables painless adoption and the shortest path to the benefits of caching
accelerated performance. For active-active applications with “bursty”
write profiles, write-back caching offers enormous performance benefits.
encapsulating all SSD processing within Mt. rainiers leaves host processor
and memory resources available to increase high-value application
processing density (for example, more transparent page sharing, more
virtual machines, and so on).
Because only one Mt. rainier is ever actively caching a LUN, and all other
members of the accelerator cluster process all i/O requests for that LUN
through that LUN cache owner, all storage accelerator cluster members
work on the same copy of data. Cache coherence is maintained without
the complexity and overhead of coordinating multiple copies of the same
data. Furthermore, by enforcing a single-copy-of-data policy, QLogic Mt.
rainier clustering efficiently uses the SSD cache; intra-cluster cache
coordination allows more storage data to be cached with fewer SSD
resources consumed. this cache utilization efficiency greatly improves the
economics of server cache deployment and, combined with guaranteed