Sans Digial TowerSTOR TS25CT
Sans Digital TowerSTOR TS25CT User Manual
7
1.3 RAID Concepts
The basic idea of RAID (Redundant Array of Independent Disks) is to combine multiple
inexpensive disk drives into an array of disk drives to obtain performance, capacity and
reliability that exceeds that of a single large drive. The array of drives appears to the
host computer as a single logical drive.
The RAID subsystem provides data striping, mirroring, XOR calculation and data
verification. It supports RAID levels 0, 1, 3, 5, 10, LARGE and CLONE. All RAID levels’
capacity can exceed 2 Terabytes. The RAID subsystem behaves as a full 48-bit
addressing RAID drive and is 100% ATA compliance.
From (PC) host controller, each logical device (RAID volume) controlled by the RAID
system acts just the same as single regular hard disk although a RAID system generally
consists of more than one hard disk drives. Therefore, no extra BIOS, driver or software
is needed.
1.3.1 Definition of RAID Levels
Striping (RAID 0) for High Performance
Striping or RAID 0
is the segmentation of logically sequential
data, such as a single file, so that segment can be assigned to
multiple hard disks in a round-robin fashion and thus written
concurrently.
Advantage of RAID 0 is to achieve high performance by
accumulating each individual hard disk performance. However,
if any one hard disk gets defective, information stored in this
RAID 0 will become invalid.
The RAID subsystem will just make use of the same disk
space for each hard disk under RAID 0 condition. For example,
if a RAID 0 consists of 5 different size hard disks, the total
usable space of this RAID 0 will be [capacity of smallest size
hard disk] * [the number of hard disks in this RAID 0].
Mirror (RAID 1) for High Security
Mirror or RAID1 is the replication of data onto separate hard
disk in real time to ensure continuous availability. In a RAID 1
system with two hard disks, the data in one hard disk will be
exactly the same as the data in the other hard disk.
The RAID subsystem will also make use of same size disk
space in each hard disk in RAID 1. That is, the RAID controller
will write data to the same disk space in each hard disk. When
reading data, the RAID controller will read data from a
specified hard disk.
Failure in a hard disk will cause the RAID controller to enter
into degraded mode. The host controller can still read/write
data to the RAID without knowing any hard disk defect. Users
have to replace the hard disk then the RAID controller will
enter in on-line rebuild mode automatically.
Besides, if there is only partial defect in a hard disk, the RAID
controller will read data from the other healthy hard drive.
