Jbod; Redundant Operation - Compaq StorageWorks RAID Array 3000 Controller Shelf User Manual

While RAID 5 is ideally suited for applications with many, small I/O
operations, there is no reason why it cannot function equally well for
applications with large, sequential I/O operations. This makes RAID 5 an
excellent all-purpose RAID level.

JBOD

JBOD makes it possible to connect one or standalone disk drives to the
controller. A JBOD disk drive is not part of a redundancy group, even though
the controller assigns a redundancy group number to the drive. This number
becomes that Logical Unit Number (LUN) that the host will use to address the
drive.
One use for JBOD is to connect a system disk drive to the controller. The drive
does not become part of a RAID set, but it is made available to the host on the
same SCSI bus as the other devices controlled by the controller.
The system parameters allow you to customize certain aspects of the controller
via the SWCC Graphical User Interface (GUI).

Redundant Operation

When operating in a redundant configuration, the two controllers are linked
such that, in case of a failure, the surviving controller can access the other
controller's cache memory and complete all operations that were in progress
when the failure occurred. The controllers support two different
configurations:
Active/Active: One host port is active on each controller. The other port
on each controller is passive and only used if the peer controller fails.
This configuration is recommended.
Active/Passive: Both host ports on one controller are active. The other
controller's ports are both passive and only used if the primary
controller fails.
When one controller fails, the survivor will process all I/O requests until
the failed controller is repaired and powered on. The subsystem will
then return to its previous state (that is, active/active or active/passive).
CAUTION: RAID 5 can withstand a single failure and handle I/O activity without
interruption in degraded mode until the failed drive is rebuilt. If a second drive
fails while the RAID set is in degraded mode, the entire RAID set will fail.
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