User manual
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Promise Technologies Pegasus J4User Manual
whAt is rAiD?
e Mac disk utility is used to create a le system for the physical drives in the J4. e section “Congure the
HardDisks”onpage15 provides a description of the procedures to create dierent RAID congurations.
Alternatively, you can simply create a le system for the disks and continue the default JBOD (Just a Bunch
of Disks) disk arrangement where each installed physical drive appears as a separate physical drive in Finder.
RAID Type
Description
RAID 0
Stripe
Data is split evenly across multiple disks, striping with no parity, no mirroring, no
error checking and no redundancy. A disk failure will destroy the array and the
probability of failure increases with the number of disk added to the array. Data
blocks are written to their respective disks simultaneously on the same sector.
This allows smaller sections of the entire chunk of data to be read off the drive in
parallel, increasing bandwidth. More disks in the array provides higher data transfer
rates, but with a greater risk of data loss. Data stored on a RAID 0 device must be
backed up on another system or the data will be lost permanently in the event of
any disk failing in the RAID 0 array.
Storage space added to the array by each disk is limited to the size of the smallest
disk, so the installed disks should be the same size. Stripe size is normally a
multiple of the hard disk sector size.
A RAID 0 array is useful for non-critical data that changes infrequently and is
frequently backed up where redundancy is unnecessary or irrelevant and when
excellent read/write performance is desirable such as audio or video streaming or
editing applications.
RAID 1
Mirror
Creates an exact copy (mirroring without parity or striping) of a set of data on two
or more disks. Used when reliability is more important than storage capacity. Can
only be as big as the smallest member disk and can only use an even number
of disks. One disk can remain inactive, as a backup and be used to rebuild the
mirrored disk.
RAID 10
Mirror / Stripe
Mirror + Stripe combines both of the RAID 1 and RAID 0 logical drive types. RAID
10 can increase performance by reading and writing data in parallel or striping,
while protecting data by duplicating it or mirroring.
A RAID 10 conguration can be created in a single J4 unit where two RAID 0
arrays — each consisting of two individual physical drives — are mirrored to
each other in a RAID 1 conguration. Alternatively, two separate J4 units — each
congured initially as a RAID 0 array — can be congured in a mirrored RAID 1 set
thus creating a RAID 10 with two J4 units.
RAID 0 or Striped RAID using all four disks on the J4
RAID 1 or Mirrored RAID creates an exact copy