Defining
the
number
of
disk
devices
on
Linux
This
section
provides
information
about
defining
the
number
of
disk
devices
on
Linux.
The
maximum
number
of
configurable
devices
that
are
available
on
supported
Linux
host
systems
is
either
128,
256,
or
2304.
The
standard
Linux
kernel
uses
a
static
major
and
minor
number
address
mechanism.
A
special
device
file
represents
each
disk
device.
For
each
default,
there
is
a
maximum
of
16
partitions
per
disk.
The
major
and
minor
numbers
are
each
8-bits.
Note:
To
determine
what
level
of
Linux
is
installed,
use
the
following
commands:
uname
-a
cat
/etc/*release*
Fibre-channel
attached
devices
are
managed
as
SCSI
devices.
Traditionally,
there
have
been
eight
major
numbers
reserved
for
SCSI
devices.
Those
major
numbers
are
8,
65,
66,
67,
68,
79,
70,
and
71.
For
kernel
levels
that
support
256
devices,
the
additional
major
numbers
are
128,
129,
130,
131,
132,
133,
134,
and
135.
Newer
kernels
are
moving
to
a
dynamic
configuration
method
that
will
use
any
available
major
numbers.
The
latest
SUSE
SLES
9
kernel
errata
include
this
change
and
impose
a
limit
of
no
more
than
144
major
numbers
allocated
to
SCSI
disk
devices.
There
are
256
minor
numbers
available
for
each
of
the
eight
major
numbers.
The
following
formula
provides
the
maximum
number
of
devices
for
Linux
host
systems:
Number
of
devices
=
(number
of
major
numbers)
x
(number
of
minor
numbers)
÷
(number
of
partitions)
.
For
example,
Number
of
devices
=
8
x
256
÷
16
=
128
or
Number
of
devices
=
144
x
256
÷
16
=
2304
.
To
set
the
maximum
number
of
disk
devices
under
Linux
to
properly
detect
all
volumes,
you
need
to
set
the
max_scsi_luns
option.
1.
Edit
the
/etc/modules.conf
file.
2.
Add
the
following
line:
options
scsi_mod
max_scsi_luns=128
.
Note:
If
you
already
have
a
max_scsi_lun
option
in
the
modules.conf
file,
ensure
that
the
values
is
set
to
128.
3.
Save
the
file.
4.
Run
mkinitrd
in
order
to
rebuild
the
ram-disk
associated
with
the
current
kernel.
You
can
use
the
following
command
as
an
example
of
what
mkinitrd
command
to
run:
mkinitrd
/boot/<image>
<kernel>
5.
Reboot
the
host.
If
you
load
a
host
adapter
device
as
a
module
in
Linux,
there
is
a
kernel
limit
to
the
total
number
of
disks
that
you
can
configure.
This
limit
might
be
less
than
the
total
supported
by
the
kernel
(usually
128
or
256).
The
first
module
that
is
loaded
on
the
system
might
configure
discovered
disks
up
to
the
maximum
number
of
disks
supported
by
the
kernel.
Subsequent
drivers
are
limited
to
configuring
a
fixed,
smaller
number
of
drives.
These
drivers
all
share
a
pool
of
device
structures
that
are
statically
allocated
after
the
first
host
adapter
driver
is
loaded.
The
number
of
allocated
device
structures
(usually
40)
is
set
with
the
CONFIG_SD_EXTRA_DEVS
108
DS6000
Host
Systems
Attachment
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Summary of Contents for System storage DS6000 Series
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