IBM DS4700 manual Redundant drive channel pair

Connecting storage expansion enclosures to the DS4700 Express

Attention

Before powering on the DS4700 Express Storage Subsystem, it must be populated with at least two E-DDMs. If at least two E-DDMs are not installed in each attached storage expansion enclosure or DS4700 Express Storage Subsystem, when you power on the DS4700 Express and its attached storage expansion enclosures, your standard storage partition key might be lost and must be regenerated using instructions on the IBM DS4000 Solutions and Premium Features Web site:

https://www-912.ibm.com/PremiumFeatures/

In addition, the resulting insufficient load to the enclosure power supplies might cause them to intermittently appear as failed, falsely indicating the power supplies are bad. All drives in the DS4700 Express Storage Subsystem and the connected storage expansion enclosure or enclosures must contain no prior configuration data.

In the initial installation of the DS4700 Express, you can add only new storage expansion enclosures to the DS4700 Express Storage Subsystem. This means there must be no existing configuration information on the storage expansion enclosures that you want to install.

If the storage expansion enclosures that you want to install currently contain logical drives or configured hot spares, and you want them to be part of the DS4700 Express Storage Subsystem configuration, refer to the IBM System Storage DS4000 Hard Drive and Storage Expansion Enclosure Installation and Migration Guide. Improper drive migration might cause loss of configuration and other storage subsystem problems. Contact your IBM technical support representative for additional information.

Redundant drive channel pair

Each controller on the DS4700 Express has a drive channel that contains two ports. The storage expansion enclosures that are connected to these two ports form a drive channel (also referred to as drive loop in certain DS4000 storage subsystem models). The maximum number of hard drives that can be installed in one drive channel is 112. One drive channel from each controller combines to form a redundant drive channel pair.

Figure 48 on page 69 shows an example of a redundant drive channel pair. If any component of the drive channel fails, the RAID controllers can still access the storage expansion enclosures in the redundant drive channel pair.

Note: In the following drive cabling figures, the DS4700 Express graphics are simplified to show only the drive ports of each controller.

68IBM System Storage DS4700 Express Storage Subsystem: Installation, User’s and Maintenance Guide