
Hewlett-Packard
that
provides
for
multiple
paths
to
a
volume,
as
well
as
static
load
balancing.
R
R0
See
track-descriptor
record.
rack
See
enclosure.
RAID
See
redundant
array
of
independent
disks.
RAID
is
also
commonly
expanded
to
redundant
array
of
inexpensive
disks.
See
also
array.
RAID
5
A
type
of
RAID
that
optimizes
cost-effective
performance
while
emphasizing
use
of
available
capacity
through
data
striping.
RAID
5
provides
fault
tolerance
for
up
to
two
failed
disk
drives
by
distributing
parity
across
all
the
drives
in
the
array
plus
one
parity
disk
drive.
The
DS8000
automatically
reserves
spare
disk
drives
when
it
assigns
arrays
to
a
device
adapter
pair
(DA
pair).
See
also
device
adapter,
RAID
10,
and
redundant
array
of
independent
disks.
RAID
6
Any
form
of
RAID
that
can
continue
to
process
read
and
write
requests
to
all
of
an
array’s
virtual
disks
in
the
presence
of
two
concurrent
disk
failures.
See
also
device
adapter,
RAID
5,
RAID
10,
and
redundant
array
of
independent
disks.
RAID
10
A
type
of
RAID
that
optimizes
high
performance
while
maintaining
fault
tolerance
for
up
to
two
failed
disk
drives
by
striping
volume
data
across
several
disk
drives
and
mirroring
the
first
set
of
disk
drives
on
an
identical
set.
The
DS8000
automatically
reserves
spare
disk
drives
when
it
assigns
arrays
to
a
device
adapter
pair
(DA
pair).
See
also
device
adapter,
RAID
5,
and
redundant
array
of
independent
disks.
random
access
A
mode
of
accessing
data
on
a
medium
in
a
manner
that
requires
the
storage
device
to
access
nonconsecutive
storage
locations
on
the
medium.
rank
One
or
more
arrays
that
are
combined
to
create
a
logically
contiguous
storage
space.
redundant
array
of
independent
disks
(RAID)
A
methodology
of
grouping
disk
drives
for
managing
disk
storage
to
insulate
data
from
a
failing
disk
drive.
refresh
FlashCopy
target
volume
An
option
(previously
called
incremental
FlashCopy)
of
the
DS8000
that
creates
a
point-in-time
data
copy
without
copying
an
entire
volume
for
each
point-in-time
copy.
Remote
Mirror
and
Copy
A
feature
of
a
storage
server
that
constantly
updates
a
secondary
copy
of
a
logical
volume
to
match
changes
made
to
a
primary
logical
volume.
The
primary
and
secondary
volumes
can
be
on
the
same
storage
server
or
on
separate
storage
servers.
See
also
Global
Mirror,
Metro
Mirror
and
Global
Copy.
remote
technical
assistance
information
network
(RETAIN)
The
initial
service
tracking
system
for
IBM
service
support,
which
captures
heartbeat
and
call-home
records.
See
also
support
catcher
and
support
catcher
telephone
number.
REQ/ACK
See
request
for
acknowledgment
and
acknowledgment.
request
for
acknowledgment
and
acknowledgment
(REQ/ACK)
A
cycle
of
communication
between
two
data
transport
devices
for
the
purpose
of
verifying
the
connection,
which
starts
with
a
request
for
acknowledgment
from
one
of
the
devices
and
ends
with
an
acknowledgment
from
the
second
device.
The
REQ
and
ACK
signals
help
to
provide
uniform
timing
to
support
synchronous
data
transfer
between
an
initiator
and
a
target.
The
objective
of
a
synchronous
data
transfer
method
is
to
minimize
the
effect
of
device
and
cable
delays.
reserved
allegiance
For
System
z,
a
relationship
that
is
created
in
a
control
unit
between
a
device
and
a
channel
path,
or
path
group,
when
the
device
completes
a
Sense
Reserve
command.
The
allegiance
causes
the
control
unit
to
guarantee
access
(that
is,
busy
status
is
not
presented)
to
the
device.
Access
is
over
the
set
of
channel
206
DS8000
User’s
Guide
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