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Port Multiplier Modes
The Port Multiplier supports individual drives (JBOD Mode), several types of RAID
and some non-RAID drive sets. Each configuration has different properties and
requirements, as follows:
JBOD Mode (Individual Drives)
Number of drives: at least 1
Unit capacity: N/A (100% of each individual drive)
Spares: no
Fault tolerance: none
JBOD mode offers all connected units to the host adapter, no RAID is defined at
all.
NOTE: JBOD mode requires a SATA controller featuring Port Multiplier support for
eSATA connections.
NOTE: Optical drives can only be configured as JBOD using an eSATA connec-
tion.
RAID 0 (Stripe set)
Number of drives: at least 2
Unit capacity: size of each member times number of members.
Spares: no
Fault tolerance: none - if any member is lost all data is lost.
RAID 0 “stripes” the file system across the array by placing “chunks” of data
sequentially between drives in a specific order.
RAID 1 or 10 (Mirror set, Stripe of mirror sets)
Number of drives: 2 (RAID 1) or 4 (RAID 10).
Unit capacity: size of one member (RAID 1) or size of two members (RAID 10).
Spares: yes – if EZ mode is not disabled and 3 (RAID 1) or 5 (RAID 10) drives are
present, the array will be initialized with a spare.
Fault tolerance: RAID 1 can withstand the loss of one drive without losing data.
RAID 10 can withstand the loss of one drive from each mirror set without losing
data.
RAID 1 works by duplicating the exact same data on two drives.
RAID 10 works by using two RAID 1 sets configured as members of a RAID 0.
Disks 1 and 2 are mirrored, disks 3 and 4 are mirrored, and the two mirror sets are
striped together.
RAID 3 (Stripe set with dedicated parity)
Number of drives: at least 3
Unit capacity: size of one member times number of members minus one.
Spares: yes
Fault tolerance: can withstand the loss of one drive without losing data.
RAID 3 works by striping data for individual I/O blocks across all members except
one, which contains parity data for the stripe set computed internally by the Port
Multiplier. In the event of failure, the missing information can be calculated using
the parity information.