The following sections describe considerations regarding the design and connectivity of the iSCSI network.
Network design is key to making sure iSCSI works properly and delivers the expected level of performance in any environment. This list defines the best practice considerations for iSCSI networks:
Use either Dell EMC PowerPath or native Linux multipathing (DM-Multipath) on all database servers. It is important that the two do not coexist on the same database server as this can cause instability.
Utilize multipathing software enabled on the database server rather than multiple connections per iSCSI session (MC/S). MC/S is not supported for PowerMax iSCSI targets.
For Linux systems using device mapper multipath (DM-Multipath), use the "Round Robin (RR)" load balancing policy. Round Robin uses an automatic path selection rotating through all available paths, enabling the load to be distributed across the configured paths. This path policy can help improve I/O throughput. For PowerMax storage systems, all available paths will be used in the Round Robin policy.
For DM-Multipath, change “path_grouping_policy” from “failover” to “multibus” in the multipath.conf file. This will allow the load to be balanced over all paths. If one path fails, the load will be balanced over the remaining paths. A “failover” policy means that only a single path will be used at a time, negating any performance benefit. Use the “multipath -l” command to ensure that all paths are in the “active” state. If paths display an “enabled” status, they are in failover mode.
For PowerPath, use the “Symmetrix Optimized” (SymOpt) policy. This is the default policy, and it means that administrators do not need to change the configuration parameters. PowerPath load-balances I/Os across all paths based on the I/O load and health state of the path for that storage device.
Figure 1. iSCSI network design for Oracle RAC