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4-1 RAID Introduction
RAID 0 (Striped)
RAID 0 reads and writes sectors of data interleaved among multiple drives. If any disk member
fails, it affects the entire array. The disk array data capacity is equal to the number of drive mem-
bers times the capacity of the smallest member. RAID 0 does not support fault tolerance.
RAID 1 (Mirror)
RAID 1 writes duplicate data onto a pair of drives and reads both sets of data in parallel. If one
of the mirrored drives suffers a mechanical failure or does not respond, the remaining drive will
continue to function. Due to redundancy, the drive capacity of the array is the capacity of the
smallest drive.
RAID 10 (Striped Mirror)
RAID 10 is a combination of striping and mirroring. This configuration provides optimal speed and
reliability, but you need four SATA hard disks.
RAID 5 (Parity)
RAID 5 provides data striping at the byte level and also stripes error correction information. This
results in excellent performance and good fault tolerance. Level 5 is one of the most popular
implementations of RAID.
RAID Ready
A "RAID Ready" system is a specific system configuration that, with the addition of a second Se
-
rial ATA hard drive, can be seamlessly migrated to a configuration that provides either improved
storage performance or data protection from a single hard drive failure.
JboD (Span)
JBOD stands for “Just a Bunch of Disks”. Each drive is accessed as if it were on a standard SCSI
host bus adapter. This is useful when a single drive configuration is needed, but it offers no speed
improvement or fault tolerance. A spanned volume is a formatted partition which data is stored
on more than one hard disk, yet appears as one volume. Unlike RAID, spanned volumes have
no fault-tolerance, so if any disk fails, the data on the whole volume could be lost. Additionally,
the system or boot partitions cannot be included in a spanned volume. FAT16/32 and NTFS file
systems may be used, and the volume can span up to 32 hard disks.
The nember of hard disks needed in different RAID level:
CA
UT
IO
N
!
RAID Level RAID 0 RAID 1 RAID 10
RAID 5
RAID Ready
JBOD
Disk NO.
>=2
2
>=4
>=3
>=1
>=1
