LSI 3ware 9750 User Manual page 19

Understanding RAID Concepts and Levels
Figure 2. RAID 0 Configuration Example
RAID 1
RAID 1 provides fault tolerance and a speed advantage over non-RAID disks.
RAID 1 also is known as a mirrored array. Mirroring is done on pairs of
drives. Mirrored disk arrays write the same data to two different drives using
RAID 1 algorithms (see Figure 3). This gives your system fault tolerance by
preserving the data on one drive if the other drive fails. Fault tolerance is a
basic requirement for critical systems should as web and database servers.
3ware firmware uses a patented TwinStor technology, on RAID 1 arrays for
improved performance during sequential read operations. With TwinStor
technology, read performance during a sequential read operation is twice the
speed of a single drive.
The adaptive algorithms in TwinStor technology boost performance by
distinguishing between random read request and sequential read requests. For
the sequential read requests generated when accessing large files, both drives
are used with the drive heads simultaneously reading alternating sections of
the file. For the smaller random transactions, the data is read by a single
optimal drive head.
Figure 3. RAID 1 Configuration Example
RAID 5
RAID 5 provides performance, fault tolerance, high capacity, and storage
efficiency. It requires a minimum of three drives and combines striping data
with parity (exclusive OR) to restore data in case of a drive failure.
Performance and efficiency increase as the number of drives in a unit
increases.
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