Dell PowerVault MD3000 - Manual (Page 52)

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Using Your RAID Enclosure
Figure 3-3. Two Hosts, each with Two Cable Connections
This cabling topology, when used with alternate path software, ensures a redundant path from the host to
the virtual disks. If any component (HBA, HBA port, cable, RAID controller module port, or RAID
controller module) fails, a host can still access the virtual disks through an alternate path.
NOTE:
This configuration is the most redundant for two hosts directly connected to a single RAID enclosure.
When a RAID Controller Module Is Replaced or Removed
When one RAID controller module fails, or is removed from the RAID enclosure, failover software on the
host directs the alternate RAID controller module to assume all controller responsibilities for the storage
array. The virtual disks owned by the failed or removed RAID controller module are failed over to the
surviving controller and no data is lost.
NOTE:
For Linux kernels, stop and then restart the SMagent after moving a controller offline, replacing a controller,
or removing SAS cables from (or attaching SAS cables to) Red Hat ® Enterprise Linux® (version 4), SUSE Linux
Enterprise Server 9 (x86_64), or SUSE Linux Enterprise Server 10 (x86_64) host servers.
Because host-based multi-path software is configured for automatic failback, the data paths and virtual
disks are restored to their original RAID controller module after the RAID controller module is replaced.
Automatic failback occurs under the following conditions:
• Data is protected by dual redundant paths to the host.
• The host has multi-path failover software installed, and it is configured for auto failback.
• Failover occurred due to either RAID controller module lockdown, replacement, or path failover.
NOTE:
Clustering requires simultaneous access from cluster nodes to shared storage. If you have clustering
software installed on the host, automatic failback should be disabled to prevent "ping-pong" with single-path
failure. For more information on clustering, a link to clustering documentation is included on the MD3000 Resource
CD
under Product Documentation.
For more information on failover, see "Cabling the Enclosure" on page 22.
dual-HBA host server
dual-HBA host server
RAID controller module 0
RAID controller module 1
MD3000 RAID Enclosure