19-06-2012, 04:14 PM
Getting Started With RAID
Getting Started With RAID.pdf (Size: 1.13 MB / Downloads: 156)
RAID Defined
RAID is a way of storing data on two or more physical disks for the purpose of redundancy,
improved performance, or both. The combined physical disks make up what is called an
array, and this array appears on the host system as one disk. For example, if you have
physical disk 1 and physical disk 2, those two disks appear to the host system as one disk.
Reasons for RAID
Depending on how you implement RAID (which RAID level you use), the benefits include
one or both of the following:
• Faster performance — In RAID 0, 10, or 50 arrays, the host system can access multiple
disks simultaneously. This improves performance because each disk in an array has to
handle only part of the request. For example, in a two-disk array, each disk needs to
provide only its part of the requested data.
• Data protection — In RAID 1, 10, 5, and 50 arrays, the data is backed up either on an
identical disk (mirror) or on multiple disks (parity disks). RAID 10 and 50 also allow
the host to access disks simultaneously.
Supported RAID Levels
Dell™ systems that use SCSI RAID controllers support RAID 0, 1, 10, 5, and 50. The
following is a brief explanation of those levels.
RAID 0 (Striping)
RAID 0, also known as striping, maps data across the physical drives in an array to create a
large virtual disk. The data is divided into consecutive segments or stripes that are written
sequentially across the drives in the array. See Figure 1-1. Each stripe has a defined size or
depth in blocks. RAID 0 provides improved performance because each drive in the array
needs to handle only part of a read or write request. However, because none of the data is
mirrored or backed up on parity drives, one drive failure makes the array inaccessible and
the data is lost permanently .