IBM DS3950, Installation, User'S, And Maintenance Manual, Page: 167 / 252

interposer card that converts the SAS drive interface protocol to a 4 Gbps FC
interface protocol. Set the DS3950 enclosure speed to 4 Gbps when these SATA
E-DDM CRUs are installed and connected to storage expansion enclosures running
at 4 Gbps speed. The link rate setting speed must be set accordingly. See “Verifying
the link rate setting” on page 138 for more information.
Do not mix 2 GB drives and 4 GB drives in the same storage subsystem. If drives
of mixed speeds reside in the storage subsystem, the data transfer rate changes
depending on the configuration. Table 21 shows the data transfer rates for drives of
different configurations.
CAUTION:
Do not change the link rate setting while the storage subsystem is running.
Changing the link rate setting while the storage subsystem is running could
cause drives to fail. You must power down the storage subsystem and storage
expansion enclosures before changing the link rate setting.
Attention: All devices on the loop must have the same data transfer rate, which
means that you must set the link rate on the storage expansion enclosure to the
same rate as the storage subsystem to which it is connected. Information about
supported DS3950 , DS4000, and DS5000 storage subsystems can be obtained from
the certified Compatibility Matrix, which can be found at the following Internet
location:
http://www.ibm.com/systems/support/storage/config/ssic/index.jsp
Table 21. Data transfer rates for drive modules
Link rate
switch
setting
Storage subsystem
with 2 GB drives Storage subsystem with 4
GB drives Storage subsystem with
mixed drives
4 Gbps Drives do not come
online. Drives work in 4 Gbps
mode. 2 GB drives do not come
online.
4 GB drives work in 4 Gbps
mode.
Before you begin, ensure that you wear an anti-static wrist strap.
Use the following procedure to check the current setting of the data transfer rate
and change it, if necessary:
1. Complete the power-off sequence described in “Turning off the storage
subsystem” on page 109 ensuring that the DS3950 storage subsystem is turned
off before any attached storage expansion enclosures.
2.
Locate the link rate indicator LEDs. Figure 81 on page 140 shows the location
of the link rate indicator lights on the back of the storage subsystem.
Chapter 5. Replacing components
139