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