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The problem with soft AL_PAs addressing is that addresses may change between
LIPs. This possibility increases the difficulty of troubleshooting drive channel
problems, since one cannot easily ascertain whether the same device with a
different address or different device may be causing a problem. IBM recommends
always setting the enclosure IDs in a given drive channel/loop pair to enforce hard
AL_PAs addressing.
Intermixing storage expansion enclosures in the same drive loop
In a DS4700 Express configuration, you can intermix EXP810s, EXP710s, and
EXP100s. When intermixing EXP810s with EXP710s or EXP100s in the same drive
loop, the Link Rate switch for all storage expansion enclosures in the intermixed
drive loop must be 2 Gbps because the EXP710 and EXP100 only operate at 2
Gbps.
There are maximum limits to the number of fibre channel hard drives that you can
configure in redundant drive channel pairs. The maximum number of drives dictates
a fixed number of supported EXP710 or EXP100 and EXP810 drive enclosure
combinations.
Table 31 lists the numbers of 14-drive and 16-drive storage expansion enclosures
you can combine for use in a single redundant drive channel/loop pair in a DS4700
Express configuration. Table 31 shows the supported storage expansion enclosures
combinations per redundant drive channel/loop pair in a DS4700 Express
configuration. The table assumes that a DS4700 Express storage subsystem is
generally capable of addressing the maximum of 112 fibre channel hard drives for
each redundant drive channel/loop pair.
Table 31. Possible combinations of 14-drive and 16-drive storage expansion enclosures per
redundant drive/channel loop pair in a DS4700 Express configuration
Number of
EXP810s
(16
drives/unit)
Total
number of
drives in
EXP810s
Number of
EXP710/
EXP100s
(14
drives/unit)
Total
number of
drives in
EXP710/
EXP100s
Total
number of
drives in
the DS4700
Express
Total number
of drives in a
mixed
EXP710s and
EXP810s drive
loop
0079816=114
1 16 5 70 16 = 102
2 32 4 56 16 = 104
3 48 3 42 16 = 106
4 64 2 28 16 = 108
5 80 1 14 16 = 110
6960016=112
For more information about intermixing storage expansion enclosures and the most
current information on the DS4000 Fibre Channel and Serial ATA (FC/SATA)
Enclosure Intermix premium feature, see the following Web site:
www-1.ibm.com/support/docview.wss?rs=1100&uid=psg1MIGR-57823
Chapter 3. Cabling the storage subsystem 99