HP A3550A - High Availability Disk Arrays Model 20 Storage Enclosure User Manual page 154

Table 4-3 Restrictions and Recommendations for Binding Disks into LUNs
Group to bind
Any group
RAID-5 group
RAID-3 group
RAID-1 mirrored pair
RAID-1/0 group
Global hot spare
Note If binding RAID-3 LUNs, follow the instructions located in the Configuring SP Memory
for RAID-3 LUNs section on page 4-28 before binding.
4-18 Creating Logical Disk Units (LUNs)
Restrictions and recommendations
Only unbound (UNB) disk modules can be bound. If you attempt 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. You can determine the capacity of a
disk module using Grid Manager by selecting that module in the
Presentation screen and pressing R
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.
Exactly five disk modules must be bound per RAID-3 LUN. Each LUN
requires a minimum of 2 MB of SP memory on each SP. For optimum
performance, 6 MB of SP memory on each SP is recommended, and only
RAID-3 LUNs should be bound in the disk array.
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.
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.
Used as a back-up for RAID-5, RAID-3, RAID-1/0 and RAID-1 LUNs. The
capacity of a disk module bound as a global hot spare must be at least as
great as the capacity of the largest disk module it might replace. The disk
modules in slots A0, A3, A4, B0, and C0 cannot be bound as hot spares
because they are the database drives that contain the SP microcode.
In addition, the disk drives in slots A0, B0, C0, D0, and E0 cannot be bound
as global hot spares if cache is installed because they are the cache vault
drives. Global hot spares should never be assigned LUN number 0. Global
hot spares are assigned a LUN number, but are not recognized as an
addressable LUN by the host.
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ETURN