Dell MD3000 owner manual When a RAID Controller Module Is Replaced or Removed

Figure 3-3. Two Hosts, each with Two Cable Connections

dual-HBA host server

	dual-HBA host server
RAID controller module 0	RAID controller module 1
	MD3000 RAID Enclosure

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.

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Using Your RAID Enclosure