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RAID 5 (Stripe set with striped 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 5 works by striping entire I/O blocks across all members of the set, with
each member taking turns carrying parity data computed by the Port Multiplier. In
the event of failure, the missing information can be calculated using the parity
information.
CLONE (Mirror set)
Number of drives: at least 2
Unit capacity: size of one member.
Spares: yes
Fault tolerance: can withstand the loss of any number of drives without losing data
as long as at least one complete member remains online. CLONE mode works the
same way as RAID 1, by maintaining a complete copy of the entire set of data on
each drive.
LARGE (Spanned set)
Number of drives: at least 2
Unit capacity: 100% of all drives together regardless of differences in size
Spares: no
Fault tolerance: cannot withstand the loss of any drives without losing data.
However, some data may be recovered as long as the drive(s) carrying the file
system data (boot record, directory, etc.) remain online. LARGE mode is neither a
RAID nor is it a JBOD. It works by declaring the sum of all available space of the
member drives as a single unit, without striping the data. As each member is filled,
new data is stored on the next.
Notes about Spare Drives
If any kind of array is defined, all individual drives not configured as array mem-
bers will be offered to the host adapter as separate units. Only the fault-tolerant
modes (RAID 1, 10, 3, 5 or CLONE) will make use of a spare – individual drives
will not be used at all and are not accessible with RAID 0 or LARGE.
To create an array with one or more spares, set or modify the RAID mode while
the spares are disconnected from the Port Multiplier. Afterward, any individual
drives connected when an array is present are considered spare. Spare drives
must be equal to or larger in size than the smallest member.
When a drive fails on a fault-tolerant RAID, if a spare is present the Port Multiplier
will automatically begin rebuilding the array onto the spare.