Disk Array - NEC Express5800 series User Manual

Disk Array

The optional disk array controller board is a PCI board that improves data reliability.
The disk array controller board allows the hard disk drives in the SCSI hard disk drive
bays and additional optional disk expansion unit to support disk array configuration
RAID levels 0, 1, and 5.
RAID is an acronym of "Redundant Arrays of Inexpensive (Independent) Disks". It
logically integrates several hard disks to appear to the system as only one disk drive.
Using the disk array method, the large-capacity hard disk can be configured with
several inexpensive and small-capacity hard disks. It can also enhance the drive by
improving the reliability and supporting an automatic rebuilding function.
All RAID levels are common in their basic operation due the fact that several hard disks
can be recognized as one disk drive. However, performance, cost, and use are
conditions that vary according to the RAID level. You should select an appropriate
configuration that is suitable for your system.
Features and selection examples of different RAID levels are shown below.
Level
RAID0
RAID1
(or shadowing)
RAID5
This unit supports other RAID levels as well. However, it is not recommended to use
them unless absolutely necessary.
1-20 System Overview
Definition Redund-
ancy
Striping No
Mirroring Yes
Striped data Yes
and parity
Feature
application
Access: high-speed. Application that
needs high
performance for
non-critical data
Dual disk system. Application that
needs to store
Read mode: high- important files
speed on main system
drive
Write mode: slower
than RAID 0
Parity data. Application that
needs to store
Transfers large
important data.
amount of data.
Application of
Write mode: slower
read-intensive
than RAID 0
type
data searching.
Suitable Minimum
No. of disks
2
2
3