IBM System Storage DS5020, Installation, User'S, And Maintenance Manual

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Verifying the link rate setting
Important: Make sure that the link rate for the DS5020 is always set to 4 Gbps.
The DS5020 supports only 4 Gbps FC drives.
If a link rate problem is indicated, use the following procedure to verify the link rate
setting.
A link rate switch is located on the front of the storage subsystem as shown in
Figure 84 on page 142. The link rate indicator LEDs are located on the back of the
storage subsystem. The link rate switch is only read when the storage subsystem is
powered up.
Note: Do not mix storage subsystems with different link rate speed settings in the
same drive loop.
The DS5020 storage subsystem drive channel operates at a 4 Gbps Fibre Channel
interface speed. The DS5020 storage subsystem SATA E-DDM CRUs have an ATA
translator card that converts E-DDM 3 Gbps SATA drive interface protocol to a 4
Gbps Fibre Channel interface protocol. The DS5020 FC-SAS E-DDM CRUs have a
FC-SAS interposer card that converts the SAS drive interface protocol to a 4 Gbps
FC interface protocol. Set the DS5020 enclosure speed to 4 Gbps when these
FC-SAS or 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” 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 DS4000 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.
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IBM System Storage DS5020 Storage Subsystem: Installation, User’s, and Maintenance Guide