HP A3550A - High Availability Disk Arrays Model 20 Storage Enclosure User Manual page 178

Group to bind Restrictions and recommendations
Any group Only unbound (UNB) disk modules can be bound. If an attempt is made to
bind a module that is binding (BIN), Grid Manager displays an error
message. All disk modules in a group must be of the same type and same
capacity to use the modules' storage space fully. The capacity of a disk
module can be determined in Grid Manager by selecting that module in the
Presentation screen and pressing R
RAID-5 group A minimum of three and a maximum of 16 disk modules must be bound.
However, for more efficient use of disk space, it is recommended that five
disk modules be bound. Note: MPE/iX has a 16-Gbyte limit for volumes
and a 4-Gbyte limit for Ldevs.
RAID-1 mirrored pair An even number of disk modules –- from a minimum of two to a maximum
of 16 – must be bound. The disk modules can be selected in any order and
each disk module in a pair should be on a separate bus. The maximum
number of disks is 16 for model 20.
RAID-1/0 group A minimum of four disk modules and an even number of modules must be
bound. Grid Manager pairs modules into mirrored images in the order that
they are selected. The first and second modules selected become a pair of
mirrored images; the third and fourth modules selected become another
mirrored pair; and so on. The first module selected in each pair is the
primary image; the second module is the secondary image.
Global hot spare Used in RAID-5, RAID-1, and RAID-1/0. The capacity of a disk module
bound as a hot spare must be at least as great as the capacity of the
largest disk module that it might replace. On a model 20, the disk modules
in slots A0, B0, C0 or A3 cannot be bound as a hot spare because they are
the database drives that contain the SP microcode.
In addition to the above, the disk drives in slots DO and EO (model 20)
cannot be bound as hot spares if cache is installed because they are cache
vault drives. Hot spares should never be assigned LUN number 0. Hot
spares are assigned a LUN number but are not recognized as an
addressable LUN by the host.
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