Dell PowerVault MD3620f Command Line Interface Manual page 125

Placing a RAID controller module online sets it to the Optimal state and
makes it active and available for I/O operations. Placing a RAID controller
module offline makes it unavailable for I/O operations and moves its disk
groups to the other RAID controller module if failover protection is enabled.
Taking a RAID controller module offline can seriously impact data integrity
and storage array operation.
If you take a RAID controller module offline, the second RAID controller
module in the pair takes over. Disk groups and their associated virtual disks
that were assigned to the offline RAID controller module are automatically
reassigned to the remaining RAID controller module.
CAUTION:
Place a RAID controller module in Service mode only under the
direction of Technical Support.
Use Service mode when you want to perform an operation, such as replacing a
RAID controller module. Placing a RAID controller module in Service mode
makes it unavailable for I/O operations. Placing a RAID controller module in
Service mode also moves the disk groups from the RAID controller module to
the second RAID controller module without affecting the disk groups'
preferred path. Moving disk groups might significantly reduce performance.
The disk groups are automatically transferred back to the preferred RAID
controller module when it is placed back online.
CAUTION:
A multipath driver is required on all hosts and is the only supported
configuration. If the multipath driver is not installed, the virtual disks are not
accessible.
Before you place a RAID controller module in Service mode, ensure that a
multipath driver is installed on all hosts using these virtual disks.
To change the operational mode of a RAID controller module, run the
following command:
set controller [(0 | 1)] availability=(online |
offline | serviceMode)
Maintaining a Storage Array
125