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40 J.D. Edwards’ OneWorld B73.3 and Windows Terminal Server
5.2.5.1 RAID Zero (RAID 0)
RAID 0 is the striping of data across a number of disks (as shown in Figure 11):
Figure 11. Example of RAID 0
When the data is striped in this manner the main benefit is performance. In
simple terms if you have four disks in a single RAID 0 array, then data access is
four times faster than retrieving the same amount of data from a single disk.
However, there is an expense for an increase in performance. If a disk should fail,
all data is lost on the array. The only way to recover this data is from a previous
backup. This is an expensive cost, in time, backup procedures, data recovery,
and also data loss. Any data entered after the last backup is lost, and has to be
reentered. A complete system reboot and data recovery must be done to bring
the system back online at the time the failure occurs.
5.2.5.2 RAID One (RAID 1)
RAID 1 is the mirroring of single disks on a single disk controller (as shown in
Figure 12):
Figure 12. Example of RAID 1
When data is written to one disk, it is also written to a second disk, thereby
creating a mirror of the data. Where RAID 0 improves performance, RAID 1
degrades performance. This is because a single write of data requires two writes
(one write to each disk in the mirror).
However, the gain is in reliability and availability of data. If a single disk fails, then
there is a complete copy of this data on the second disk. Recovery in this
circumstance is to simply switch to the other disk (this may require a reboot of the
system). Once back online you replace the failed disk, and reinitiate the mirror to
bring things back to normal.
RAID-0
Non-Fault Tolerant
data1
data5
data9
data2
data6
data10
data3
data7
data11
data4
data8
data12
5842\RAID0
RAID-1
Fault Tolerant
data1
data2
data1
data2
5842\RAID1A