IBM System Storage DS4000 EXP420 Installation, User And Maintenance Instructions page 105

For proper cooling and EMC protection, do not leave a drive slot open without
either a drive blank or a EV-DDM CRU inserted.
v EV-DDM CRUs:
– In this release, 2 or 4 Gbps fibre channel EV-DDMs are supported. The Link
Rate setting speed must be set accordingly. See "Verifying the Link Rate
setting " on page 86 for more information.
– IBM recommends that when adding EV-DDM CRUs, if you are not installing
all 16 EV-DDM CRUs into the EXP420, install the EV-DDM CRUs from left to
right consecutively.
– For optimum performance, never insert a EV-DDM into a storage expansion
enclosure without first confirming the drive firmware level. Contact IBM
Support for information on supported drive firmware levels.
– Use of non-supported drives in the drive expansion enclosures can cause the
storage expansion enclosure to fail.
– In configurations with mixed drive expansion enclosures, all enclosures on a
fibre loop must be operating at the same interface speed.
– Ensure that the speed of the drive CRU you are adding is supported in the
storage expansion enclosure. For example, do not install a 2 Gbps drive CRU
in a storage expansion enclosure that supports only 4 Gbps drives.
Note: The EXP420 SATA EV-DDM CRUs have an ATA translator card that
converts EV-DDM 3 Gbps SATA drive interface protocol to either 2 or 4
Gbps fibre channel interface protocol.
– Drive CRUs are not interchangeable between EXP810s and EXP420s.
– After you remove a EV-DDM CRU, wait 70 seconds before replacing or
reseating it to allow it to properly spin down. Failure to do so may cause
undesired events.
Attention
Before you power on the DS4200 Express Storage Subsystem, the DS4200
Express must be cabled to at least one storage expansion enclosure
populated with at least two EV-DDMs. If at least two drives are not installed
in each attached storage expansion enclosure when you power on the
DS4200 Express, your standard storage partition key will be lost and will
need to be regenerated using instructions on the IBM DS4000 Solutions
and Premium Features Web site:
https://www-912.ibm.com/PremiumFeatures/
Additionally, if at least two drives are not installed in each attached storage
expansion enclosure, the resulting insufficient load to the storage expansion
enclosure power supply CRUs might cause the drive expansion enclosure
power supply CRUs to intermittently appear as failed and then reappear in
an optimal state, falsely indicating that the power supply CRUs are bad.
v EV-DDM CRU labels: A label is provided on the front of each EV-DDM. Use this
label to record the location information for each EV-DDM before you remove it.
Ensure that you keep track of the EV-DDMs and their corresponding bays. Also,
record the location information in Table 27 on page 112. If you install an EV-DDM
in the wrong bay, you might lose data.
Chapter 5. Installing and replacing devices
77